I am lost in this : Define src_ptr and dest_ptr at address 0x20001000 & 0x20002000 without assembler directives. What should I do?
So review your class notes, and recommended reading.
If you're still stuck, then you need to go back to your teacher and ask her/him to explain it again.
I know the method of directives and storing them, Like var DCB 0x21 on location 20000000 but I don't know how to do without directive such that a particular address has var value.
Context dude, context. We have no idea what your class or assignment is asking. Please learn to formulate questions.
src_ptr EQU 0x20001000 ; ??
If you don't know how to do your homework, then you really need to talk to your teacher about that.