Very simple. Load any Trial of War that starts with 20 random Uruk Captains. You should have no intel, thus, allowing for twenty generic Uruks to be solicited for intel. After you have interrogated (gain intel), followed by killing the Uruk, 20 soldiers, exit out and reload. This will give you another twenty and after ten, the challenge is yours!
Note: If you already have all intel or close to it in any area, dominating an Uruk will replace the "get intel" option with a "kill" option. This works as well.