Definitely. I don't see why not. In many universities, an end-of-semster online survey/questionniare is regularly administered to gain feedback from students about their learning experience. This kind of survey/questionnaire can be translated into another format in which the learners/students evaluate their teachers'/instructors' scope of knowledge in their domains of expertise. Here are some examples I recommend: (i) "The teacher explains the lecture materials in a clear and comprehensive manner." (ii) "The teacher elucidates hard-to-grasp concepts/theories with examples of their real-world application," (iii) The teacher encourages us to read beyond the textbook and topics of examination."

Hope that my response helps.

By content knowledge, do you mean the teacher appear knowledgeable, then asking students is reasonable if you believe they can judge this (if the teacher confidently says something that isn't true, then this might not pick it up). If you mean content knowledge by something like if they are teaching Algebra I do they know Algebra II well, then giving them the Algebra II test makes sense. So the answer depends on what you mean. Can you tell us more about what you mean by "content knowledge?"

Content knowledge is found to be a crucial part of the knowledge base for teaching and very closely related to student  increased learning, motivation, and interest. The teachers content knowledge can be measured by exploring the questions related to Curriculum knowledge , Subject matter knowledge , Knowledge of students , Teaching strategies knowledge  as well as Knowledge of teaching and learning evaluation . the following link  may be more usefull in developing the construct for the study.

http://ac.els-cdn.com/S1877042810022366/1-s2.0-S1877042810022366-main.pdf?_tid=c0e3a9fc-683b-11e7-8a2f-00000aacb35f&acdnat=1499999330_1d4a9232b3ea6186d58be33759c402b2

Thanks for your contribution. Dr.Dhani explained quite clearly

Of course YES.

Hi 

Yes you can measure it either by using questionnaire consists of a number of items related to the subject under investigation. On the other hand you can used a test with closed ended questions  and multiple choice items. Both of these ways must be based on the table of specification of the whole content material. 

Liqaa 

I am not sure if everyone understood your question very well or perhaps I have a different view. I think you are asking whether we can judge a teacher's content knowledge by just using a questionnaire tool?..if this is the case I would say yes to an extent, but not with certainty

Thanks Vikas! What do you mean  " but not with certainty"?

I would say that content knowledge of a teacher can be judged through the use of a student questionnaire.  My university routinely asks student's opinion of the content knowledge of teachers.  Yet, in my thinking, these are judgments, and may not be actual measures of content knowledge.  Students in this case would be consumers of knowledge.  Asking the consumer may or may not reflect actual knowledge.  The consumer would judge knowledge through their own lens.  I am always interested in what students think of my content knowledge.