It's always better to speak from the context)

Nevertheless, 'I wonder' usually has the meaning of 'I'd like to know'

here's an example:
'When he phoned me two days ago he was telling me a long story about why he had been late for school. At that time I was wondering if he was really delayed'
I mean that at that time I was thinking if he was telling the truth. Some time later, I either learnt the truth or lost interest in that matter.

some useful notes:

- in such sentences 'if' is usually translated into Russian as 'ли'
- mind the tenses:
I wonder - present simple
I wondered - past simple
I was wondering - past continuous