What do you want to cover with this question? Here’s a checklist...
✔ Where did they go to find a solution?
✔ How long did it take to make the decision and buy?
✔ Whom did they consult to make the decision?
✔ What alternative(s) did they consider?
✔ What persuaded them to buy?
✔ What, if anything, nearly stopped them from buying?
Important: remember to ask ‘why!’ ‘Why’ is the magic word that will get them to dive deeper into their experience and offer meaningful insights rather than short replies.