We use 'do' in questions when the subject is you, we, they or I (ty, my, oni, ja).
They speak English.
Do they speak English?
I have a black notebook.
Do I have a black notebook?
If the subject is he, she, it (on, ona, ono) we use 'does'.
She likes icecream.
Does she like icecream?
He studies history.
Does he study history?
Remember!You don't use 'do' and 'does' in questions that contain 'can', 'must', 'might' and 'should.'
(such as; Can you speak German? Should he wear that hat?)