Unlike other layout editors, you can select shapes inside of a cell instance, and do things with them like "copy". . . but you can't move them because they're not in the edit cell, they're inside a subcell. So what you want to do is to select the instance itself, not the stuff inside it. Use the

i

key (command

select cell

) to select the instance, or the

s

key also works if you have the cursor over empty space inside of the cell.

I am trying to do the same. But it seems to be selecting the top cell. I press "i" key after selecting the bbox containing the nmos , its selecting the top cell rather than nmos