Study with an Elder - propose a question.
Ask him why "leukozytes", white blood cells are forbidden for medical use of a JW.
On the other hand for newborn babies, there are more leukozytes in mothermilk than in the same amount of blood.
On another thread the poster , yizuman points out how many times the WT flip flopped as to whether the men of Sodom & Gomorrah would be resurrected.And he lists the publications to verify it.
I think that would be a good question to ask him along with when is the "truth" the real "truth" and how can the Holy Spirit give such conflicting opposing "truths" in a matter of a few decades.?
Ask him how he can be certain that Holy Spirit directs their teaching, then ask when they change doctrine does that mean no Holy Spirit was involved in original teaching.
Get him to explain Luke 10:7. Should be amusing.