Reported questions with ли

To report a yes/no question, Russian puts the particle ли straight after the word being asked about, usually the verb: Он спросил, знаю ли я его адрес (He asked if I knew his address). Never use если for this kind of if.

Russian keeps the tense of the original question. He asked «Ты знаешь мой адрес?», so the report says знаю ли я, even though спросил is past. In the same way:

• future stays future: Мы не знали, успеем ли мы на поезд (We didn't know whether we would make the train).
• past stays past: Она не помнит, закрыла ли она дверь (She doesn't remember whether she closed the door).

Only the person changes as usual (ты → я). Put a comma before the verb with ли.