Vedas speak of the oneness of existence, not that there is only one God.

...only thing I do not like or watch is when he [Dr. Zakir Naik] debates with other religions and embarasses them by showing them bits from their books.

That's true, he quotes only 'bits' from, say, the Vedas, and claims that the Vedas say there is only one God when the whole of the Vedas speak of the oneness of existence, not that there is only one God.