Oh man, this stuff hits me for sure.
My dad and I were never 'best friends' at all. But the relationship has gotten better over the years.
Quick question....My dad is what you may call agnostic. Never really talked to him about God just because our conversations never get too deep.
What do you think would be a good way to witness to him?
Just love him. If he sees the influence of Jesus in you, you won't have to try real hard. Use casual conversations to ask his opinion on things. Most people make bold statements and assertions hoping that will change people's minds. It never does. Instead, find out what he thinks. Ask him questions and try to understand where he's at. After a little time, you'll have enough information that you can research answers to his most pressing questions. Just don't badger him about it. That tends to push people away.