in the Noahide laws, what does it mean to deny God? (asking jews)?

According to the Jewish belief --

Before "The Messianic Time" non-Jews are only faulted (in the Divine court) for failing to practice those Noahide laws that are naturally observable -- the laws of kindness and justice.

A person who is an Atheist or a Polytheist or ...really has any religious beliefs can therefore be considered among "the righteous among the nations" --

some of the people specifically acknowledged as such by the Jewish sages include

Alexander the Great

Emperor Marcus Aurelius

Pope John Paul II

once comes The Messianic Time, then the knowledge of God in the Jewish ethical monotheist manner will likewise become naturally observable -- and at that point -- all human beings will be obligated in it as well.

In the present, however, there is a second level of those who affirmatively want to make themselves obligated to the covenant of Noah.

A person who wants to affirmatively seek out God by following the Jewish teachings and take up the full "Noahide Covenant" must be monotheist.

You can't have an Atheist or a Polytheist or a follower of some religions which define God in a fundamentally different manner from Judaism who can at the same time affirmatively call himself a Noahide.

see EXODUS 20...THEY HAVE THE SAME TEN COMMANDS.