Student or Learner
When in court, do we say " a lawyer for prosecution" or " a lawer for defense"?
In the US, you can refer to the prosecutor or the district attorney, or the state's counsel.
The attorney/lawyer/counsel for the defense is okay.
That assume a criminal trial. In a civil trial, you have a plaintiff and a defendant.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
And you can say defence/defense lawyer.
You can also just say the defence, in BrE anyway.