There isn’t a best way. A conversation is a conversation. It’s pretty obvious that when he or she stutters to not make a big deal out of it. You can ask if he has a stutter but say it in a “wow I am shocked but it kinda interests me a bit” tone of voice if your trying to get that person to like you. Basically be chill about it and keep the convo going even when they stutter. A stutterer who doesn’t want to stutter are the easy ones to point out and are usually more easier to talk too. Hey. Good luck.