Friend or partner usually works but there's other more cute fun things but if your not sure just basic is the way to go and as always. Ask them what they want but in a casual genuine way.
That's a question my very partner asked me! It's hard, and I think everyone has different terms they prefer. In my case, I love to know how the other person see me, what characteristics they like about me. So I've got my fair share of weird/wonderful nicknames, and they're special because each person made a little story about it, you know?
But, some of the more usual ones are honey, babe, love, sweetheart. I love when people see me as soft/caring, so I quite like those! 💜
Now, talking as someone who has lots of enby friends: ask them! I've seen some people say that asking feels weird or forced, but I think it's a way to show you care about them 💜 I'm glad when people ask me how I'd like to be called, because they're being thoughtful of how I feel, and really, that's a huge green flag to me :D
Pet names are very intimate and rarely gendered. I often refer to my partner as poppet - go ahead and guess their gender.
In terms of work acquaintances I think your question is even weirder. Please don't call your coworkers babe or hunk - names are nice and you should default to using them unless they offer up a nickname and both of you are comfortable with them.
If I’m giving a coworker a nickname, it is usually some riff off of their real name that I know they don’t mind. This should be asked directly after creating it, and not just assumed. Most work friends won’t mind a humorous alternate name that is deployed sparingly and in private.
Not non-binary, but I'm a man of respect and I prefer to be addressed as Padrino.
