In The Sims Medieval, you need quest points in order to unlock new quests. You normally get them by doing quests, but you can enter a cheat to set however many quest points you want.
Hit Ctrl+Shift+C to bring up the cheat console at the top of the screen. Type in setqp followed by a number, then press enter to set your quest points to that number. For example, if you type setqp 100 and press enter, you’ll now have 100 quest points.