What can the best method be used to assess the level of Knowledge, attitude, and practice of public toward their disease ?. Is it recommended to usually use scoring method ,or are there any alternative method ?
A survey questionnaire with simple and concise concepts should suffice but if you really want to use scores I believe you will have to apply existing scoring questionnaires and compare outcomes from your study population.
There already is a large literature on KAP, so you certainly could use or adapt one of those existing scales to your specific topic.
If you want to go beyond scoring, you could consider a mixed methods approach, where you also collect qualitative data. In particular, you could begin by producing quantitative findings, and then exploring them further with a set of qualitative interviews, which is known as an explanatory sequential design (QUAN --> qual).
I strongly recommend for using standard questionnaire which were already validated in your context instead of preparing survey schedule. If you prepare schedule then there may arise questions in psychometric properties of tool, so if you use already validated tool then you will be out of those hurdles.