I wonder if / whether I can get some advice from you.
Ask him whether / if he can come.
正：Let me know whether you can come or not.
误：Let me know if you can come or not.
正：Whether it is true or not,I can’t tell.
误：If it is true or not,I can’t tell.
正：I don’t know whether to accept or refuse.
误：I don’t know if to accept or refuse.
正：I worry about whether I hurt her feelings.
误：I worry about if I hurt her feelings.
正：It was uncertain whether he would come.
误：It was uncertain if he would come.
正：His first question was whether Tom had arrived yet.
误：His first question was if Tom had arrived yet.
正：We must consider the question whether we will take these measures.
误：We must consider the question if we will take these measures.