I saw a new flower pot at Susan's house today. So if i want to ask her when she bought the flower pot, how should i ask her?

If I asked her,

When did you buy the flower pot?

Can i use did in this sentence?
I usually listen tha songm "When Did Your Heart Go Missing?".
So yes.
Yes, you can. The sentence you have created is correct. You are asking about an action completed in the past, so the past tense is correct.