is it correct if I write " you can’t smoke in here " ?
If it’s a sentence, it needs a capital letter and full stop, otherwise it’s fine.
I couldn’t find out.what is the difference between here and in here?
how does it make sense?can i smoke in here?
can we say,can i smoke in? saying inside the room or bar!
Yes, the difference is that ‘in here’ usually applies to an enclosed space (inside the place).
‘here’ just indicates where you are indicating.