Ask them why they are trying to change the subject.
99% of the time, when you walk away from a JW feeling like you lost.....
.... It is because they changed the subject to something they feel more comfortable with.
Restate your question.
Act offended that they are trying to divert you from your subject.
If the tactic they are using is something they have accused another religionist of..... remind them. Every time they try to use a double standard ... point it out and act offended that they should stoop to such depths discussing their beliefs with you, their precious son/daughter/sibling/grandparent/whatever...... then restate your question.
Remind them..... It is your question that is important. If they ever want to have any chance of saving you from their killer god, who they say is going to kill you in the very near future, they have to have a legitimate answer to your question ....