In casual speak, I usually say "what's the word," tilt my head upward, and start snapping my fingers when I'm thinking of the right word. Sometimes, when I know I don't have the correct word in advance, I will say "for lack of a better word" and then follow that up with a substituted word while using my fingers to quote it. I hope this helps answer your question. Please let me know if it doesn't =)

'It went blank' doesnt make sense however you could say 'my mind's gone blank' which makes perfect sense and is the first thing i would say

I usually say, "Oh, what was the word? It was right there (on the tip of my tongue)..." or the third option, "I have it in my head but I can't think of it right now." All of the options seem fine to me aside from a few errors. -I can't remember it -I can't think of it off the top of my head (this seems better to me than "I can't think of it offhand", that doesn't sound natural to me) -I have it in my head but I can’t think of it right now -It went blank (as Marie said, this is not used very often, I've never heard it before) -I can’t think of it, it was in my mind a minute ago -I got nothing -I'm trying to remember it but I'm drawing a blank.

"I got nothing" and "it went blank" is not used very often but I would still understand you if you said it. Other than that, the other options sound natural. If you really can't remember it, try describing it. If not you can say , " I'll get back to that later".

I think don't afraid of laughting from someone when u said smthin wrong in English. Be brave.