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 ?
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