I think that it really comes down to the witness that you talk to. What got me was that someone asked about my beliefs, and I explained it to them. Then they would say, "but what do you think about this specific thing that directly conflicts with what you believe about reality?" The person I talked with gave me exact names of things I could look up for myself.

Now this is where the onus comes onto the witness. I had to go home and say to myself "you know what, I'm going to look up what Joe Blow was discussing with me, so I can find an answer to that." As witnesses we were told to do this, to increase our faith and to have answers to questions others ask about our faith.

However, some topics are undeniably impossible for a witness to have an answer to. Anything science based that conflicts with Genesis's creation account, or Noah's flood is good. Those things are undeniable if the witness is really honest with themself. And even if they deny it to you, inside their own head the information settles in and stays forever.