I was able to prove just about every one of their teachings wrong to myself using just the Bible and common sense. Take for example the blood doctrine, they use a scripture in Acts to say it’s a valid doctrine and wasn’t lost to the new covenant.
But one can easily use the scriptures to point out that jesus said “nothing entering into a man can defile him,” “we desire mercy not sacrifice, “ saying it was ok to break the laws of the covenant if it was to save life.
Then there the scriptures in later New Testament writtings where Paul says it ok in Corinthians and I believe Colossians to go ahead and eat bloody meat. Last but not least can’t remember the book but Peter is given a vision of a table full of unclean things and is told it’s ok to partake, destroying the Jewish ideas on what and not what to eat.
These scriptures with out even going into the Old Testament prove thier blood doctrine wrong but most JWs won’t see it because thier thinking ability has been removed from them.