Learn Turkish: Tok musun?

In Turkish yes/no questions, personal endings (like -sun for "you") attach directly to the question particle (mı/mi/mu/mü), not to the main adjective. So instead of "toksun mu", it is always tok musun.

Why do we use mu here instead of mi?

The question particle follows 4-way vowel harmony. Since the only vowel in tok is 'o', the rule dictates that the following vowel must be 'u'. That makes the question particle mu.

Can I use tok to say a glass or a room is full?

No, tok is only used to describe a person or animal that is "full" (not hungry) after eating. If you want to say an object is full, you would use a completely different word (dolu).

Where is the word for "you" (sen) in this sentence?

The -sun suffix at the end of musun already tells us the subject is "you" (singular informal). You could say Sen tok musun?, but Turkish speakers usually drop the pronoun unless they want to add special emphasis.