I wonder if...?
Is the expression "I wonder if..." correct in english?

Reading an english book I realised that they use "I wonder whether..." to ask something themselves.
Can both expressions be used equally ?

Question

I wonder if...?
Is the expression "I wonder if..." correct in english?

Reading an english book I realised that they use "I wonder whether..." to ask something themselves. 
Can both expressions be used equally ?

Answer

For expressions like this, just search for the phrase, with quotation marks. Then you'll find examples if it's correct.

(Spoiler: yes)

Same story with difference between words. Search: difference if whether

Bonus: http://www.quickanddirtytips.com/education/grammar/if-versus-whether

Answer

Yes, you can certainly say 'I wonder if'.