This is an affirmative sentence: "Sen çok çay içiyorsun."

These are the components of içiyorsun:  

iç: verb stem

iyor: present continuous tense suffix

sun: personal suffix for second person singular .

This is a question sentence: "Sen çok çay içiyor musun?"

Notice how we have moved the personal suffix after the question suffix. Future tense and Present Continuous Tense work that way and both use the same set of personal suffixes. Simple Past Tense doesn´t work like this. In Simple Past Tense we put the question suffix to the end. Also Simple Past Tense uses its own set of personal suffixes.

Exercises:

Turn each sentence into a question sentence.

Example:

This is the given sentence: "Sen çok çay içiyorsun."

This is your answer: "Sen çok çay içiyor musun?"

This time the answer is given but the question is missing. Build a question for each given sentence.

Example:

This is the given sentence: "Hayır, ben çay içmiyorum."

This is your answer: "Sen çay içiyor musun?"