Answer:
needs
Step-by-step explanation:
To find the verb, first find the prepositional phrases and cross them out. "on the stove" is a prepositional phrase, "in the pot" is one, and so is "to be stirred," so you know the verb is not part of those. You are left with "The spaghetti sauce needs". Since "the spaghetti sauce" is the subject of the sentence, "needs" is the verb.
Hope this helps! Let me know if you have any confusion!