There are two main ways of asking questions – directly and indirectly. Both have the same meaning but we use indirect questions when we want to be more polite or more formal.

Construction:

   Polite phrase (Do you know… / Could you tell me… / I don’t know… etc ) + Sub + Verb (do, worked, has worked, didn’t know, doesn’t work, hasn’t done). 

   Use IF or Whether when there is no question word (when, how, why, etc…)

Examples:

Direct – Where has Tim gone?
Indirect – Do you know where Time has gone? (NOT Do you know where has Time gone?)

Direct: Who is he?
Indirect: I don’t know who he is. (NOT I don’t know who is he)

Direct: Did he like the idea?
Indirect: I don’t know IF he liked the idea