Learn Turkish: Siz avukat mısınız?

To make a yes/no question with "to be", we take the question word (mı) and attach the personal ending for "you" (-sınız) directly to it. So, mı (is it?) + sınız (you) makes mısınız (are you?).

Why is the question word mısınız instead of misiniz?

It follows vowel harmony based on the word right before it. The last vowel in avukat is "a", so the question particle must use an "ı", making it mı. Then, the personal ending (-sınız) also matches that "ı".

Siz usually means plural "you" (you all), but the translation says "a lawyer". Why?

In Turkish, siz is used for the plural "you", but it is also used as a polite, formal "you" for a single person. Because the translation says "a lawyer" (singular), we know the speaker is politely addressing one person.

Why isn't there a word for "a" (bir) in the Turkish sentence?

When stating or asking about someone's profession, Turkish usually drops the word bir (a/an). You just use the noun directly, so you ask avukat mısınız? rather than bir avukat mısınız?.