This is a topic I am interested in.
Scripture says: “If they do not listen to Moses and the prophets, they will not be convinced even if someone rises from the dead.” - Luke 16:31
How I interpret this (as someone who is neither a priest or a theologian), is that no amount of philosophical arguments can convince someone of the divinity of Jesus. The Pharisees didn't even believe the divinity of Jesus when He was performing miracles in front of their very own eyes. I believe that faith comes from obedience and purity.
If someone really desires to tell someone a specific string of words to unlock someone else's belief in God, I believe their best bet is to tell the atheist/agnostic to read scripture, while the Christian does their best to lead a Christlike lifestyle, which can be shown through the Protestant work ethic
However, I am of the opinion that the entire concept of atheism is a myth.
"Their end is destruction, their god is their belly, and they glory in their shame, with minds set on earthly things.” - Philippians 3:19.
This shows that even so-called atheists can worship their own lower, false gods. Which means the Reddit atheist argument of "I just worship one less god than you do" has zero merit.
In other words, it's possible to be A-christian, but under Christianity's framework, it is not even possible to be a-theist, since atheists worship other things besides Christ (such as video games, anime, porn, etc;)