i want to level with my friend equally but i switch to death knight and the starting zone already give me so much EXP.
either i want to stop getting EXP entirely and resume it later once my friend is on the same level as me or is there a way to make it so that i get very little EXP.
thank you
That would be your only choice for now. You can stop EXP completely when you reach your faction's capital at the end of the DK quests.
An NPC (located in the Stormwind or Orgrimmar battlerooms, for Horde: Slahtz, for Alliance: Behsten) will on request stop your XP. This will cost 10 gold to disable, and 10 gold to enable again. I think both NPC's were stealthed Rogues, so spotting them may take a bit.
You can also spend points to faction swap which will port you out of dk starting zone and into Orgrimmar or Stormwind. You will skip all quests, be awarded all talents, and still be the same level you were before the faction swap.