Hello, Wael Shaltoot,
They asked me........ I wanted coffee or tea. (if_whether_whether not_that)
I do know "whether" is OK. Yet, what about"if"?
Yes, both "whether" and "if" are correct, but they are different.
With "whether," the person was asked if he/she wanted either coffee or tea, i.e. one of the two.
With "if," the noun phrase "coffee or tea" is equivalent to "something hot to drink." There, the conjunction "or" does not exclude one of the two drinks as it does if "whether" is used.