Knowledge , Attitude and Practice study  is it self a cross-sectional study or you can say that KAP is a part of cross-sectional study 

Hence the Advantage and Disadvantage of KAP study will be same as that of cross-sectional study.

Advantage of cross sectional study 

1. cost effective 

2.  not time consuming

3. At a particular duration a snapshot or picture of either exposed or unexposed or outcome present or absent  is obtained

4. Perhaps the only study which you can estimate the prevalence but that depends what type of setting from which sample size is obtained. For a tertiary hospital its not possible to estimate prevalence but for school or village or Primary Health care centre its possible as the pt coming to the hospital are not representative of the population whereas the participants of Primary Health centre  or village is representative

Disadvantage

1. Temporal bias

2. Survival bias ( depends on what  is the topic especial chronic respiratory or vascular disease or diabetes etc.)

Further for advantage and disadvantage of KAP study  i think you should refer to Leon Gordis and HENEKEINZ 

You can get more on KAP from a text book of behavioural epidemiology 

Hope its useful 

Hope it will help

Brief Description: A Knowledge, Attitude and Practices (KAP) survey is a quantitative method (predefined questions formatted in standardized questionnaires) that provides access to quantitative and qualitative information. KAP surveys reveal misconceptions or misunderstandings that may represent obstacles to the activities that we would like to implement and potential barriers to behavior change. Note that a KAP survey essentially records an “opinion” and is based on the “declarative” (i.e., statements). In other words, the KAP survey reveals what was said, but there may be considerable gaps between what is said and what is done.

Uses: A KAP survey can:

• Measure the extent of a known situation; confirm or disprove a hypothesis; provide new tangents of a situation’s reality.
• Enhance the knowledge, attitude, and practices of specific themes; identify what is known and done about various health-related subjects.
• Establish the baseline (reference value) for use in future assessments and help measure the effectiveness of health education activities ability to change health-related behaviors.
• Suggest an intervention strategy that reflects specific local circumstances and the cultural factors that influence them; plan activities that are suited to the respective population involved. 

Tool Components:

OPERATIONS

Number of Staff Required: The team will be composed of surveyors and supervisors. The number of supervisors is directly dependent on the number of surveyors, which is determined by the size of the survey and the resources available. Each supervisor should have daily face-to-face contact with each of the surveyors that s/he supervises. For 10-15 surveyors, for example, two supervisors work quite well.

Time: A KAP survey takes between six and twelve weeks. 

Cost of Assessment: This will vary depending on the context and the number of respondents. It is critical to not to underestimate the magnitude of resources and time necessary for the implementation of KAP surveys, which are costly and time-consuming.

Training: Training surveyors is crucial. The training lasts two-to-four days depending on the complexity of the survey and questionnaire and the experience level of surveyors recruited. The training should allow surveyors to master the knowledge, skills, and expertise specific to the KAP survey.

Geographic Targeting: A KAP survey is conducted on a specific target population; respondents are randomly selected from a complete sampling frame. The target group may share common characteristics, such as youth under 18 years old, artisans, or drug users (here the KAP questionnaires are aimed at individuals), or a more general population, e.g. a region or village (questionnaires aimed at households).

Type of Data Collection: A KAP survey uses household and individual surveys. 

Degree of Technical Difficulty: KAP surveys vary; the complexity will be determined by the specific questions included in a given survey.

Complements other Resources: Open-ended interviews and focus groups can complement a KAP survey, allowing further exploration of a situation or problem, and potentially highlighting aspects that are not yet known. These methods combine observations and open interviews and help deepen topics addressed in the KAP survey.

There is increasing recognition within the international aid community that improving the health of poor people across the world depends upon adequate understanding of the socio-cultural and economic aspects of the context in which public health programmes are implemented. Such information has typically been gathered through various types of cross-sectional surveys, the most popular and widely used being the knowledge, attitude, and practice (KAP) survey, also called the knowledge, attitude, behaviour and practice (KABP) survey (Green 2001, Hausmann-Muela et al. 2003, Manderson and Aaby 1992, Nichter 2008:6-7).

https://www.anthropologymatters.com/index.php/anth_matters/article/view/31/53

Guideline for Conducting a Knowledge, Attitude and Practice (KAP) Study

“KAP” study measures the Knowledge, Attitude and Practices of a community. It serves as an educational diagnosis of the community. The main purpose of this KAP study is to explore changes in Knowledge, Attitude and Practices of the community, paramedical personnel and medical practitioners on diabetes and diabetic retinopathy. This study will provide information for valuation of the diabetic retinopathy programme. It reveals increases in knowledge, changes in attitudes towards diabetes and diabetic retinopathy, as well as changes in the kinds of practices that are followed regarding management of diabetes and diabetic retinopathy.

The attractiveness of KAP surveys is attributable to characteristics such as an easy design, quantifiable data, ease of interpretation and concise presentation of results, generalisability of small sample results to a wider population, cross-cultural comparability, speed of implementation, and the ease with which one can train numerators (Bhattacharyya 1997, Stone and Campbell 1984).

KAP surveys measure the extent of a known situation; confirm or disprove a hypothesis; provide new tangents of a situation’s reality. • Enhance the knowledge, attitude, and practices of specific themes; identify what is known and done about various health-related subjects. • Establish the baseline (reference value) for use in future assessments and help measure the effectiveness of health education activities ability to change health-related behaviors. • Suggest an intervention strategy that reflects specific local circumstances and the cultural factors that influence them; plan activities that are suited to the respective population involved.

A GUIDE TO DEVELOPING KNOWLEDGE, ATTITUDE AND PRACTICE SURVEYS

A KAP survey is a representative study of a specific population to collect information on what is known, believed and done in relation to a particular topic

http://apps.who.int/iris/bitstream/handle/10665/43790/9789241596176_eng.pdf;jsessionid=303333C15310CE137E07225C2839A930?sequence=1

The KAP survey investigates

Knowledge: Does the trainee know what to do (i.e., does s/ he remember the key points of the training?)

Attitude: Does the trainee think the technology is suitable for her/ him (and if not, why not)?

Practice: Is the trainee actually going to implement the new technology?

Why use KAP?

The KAP survey has several immediate advantages. It is particularly easy to use where technologies are disseminated through organised training events like training sessions, demonstrations and field days. The questionnaire is short and sample size is small, so KAP data can be processed quickly and easily using a computer, calculator or hand tabulation.

KAP serves a double function: 1. In the case of positive findings (understanding and adoption of activity), it provides the earliest evidence of probable future project benefits and it is reasonable to presume that longer term outcomes and impacts such as increased income, more secure livelihoods, etc. will follow in due course. 2. In the case of negative findings,

KAP provides an early warning that there are problems, either with the technology or with the training methods.

https://asia.ifad.org/c/document_library/get_file?uuid=f4381104-a6c1-4249-bef5-761e32209cb0&groupId=627927