Start with the symptom you see on the board. Each answer narrows the branch — one follow-up question routes you from a defect family to the specific likely cause, then gives you what to check and how to fix it.
Start by observing the defect precisely, bound where and when it happens, stratify by board / position / lot, examine the process step responsible, recreate it on demand, verify the fix with data, then prevent recurrence with a control.