what does it mean to challenged a belief? (Please give the short simple answer & example).?

Let's say, for example, someone holds firmly to the belief that the Earth is flat.

One might "challenge" that belief by presenting his or her interlocutor with the evidence of the many circumnavigations of the Planet Earth, terrestrial and celestial.

https://en.wikipedia.org/wiki/List_of_circumnavigations

One's interlocutor might still cling to the (frankly, obviously erroneous) belief (people are stubborn that way), but nevertheless, the belief, to the mind of most sentient beings, has been successfully "challenged."

Que

It means to question or contradict a belief another holds. A good example is Hillary Clinton's comment about Trump believing climate change is a hoax created by the Chinese.

it means to present an objection or query as to the truth of the belief, often with an implicit demand for proof. Example: You say you believe you can lift 200 lbs, let's see you lift this set of dumbells which weigh 200lbs.