How to recognize original display of iPhone 6s
How to recognise original iPhone 6s display?
iPhone 6s, iOS 14
Are you asking does your iPhone 6 have its original display screen or it is a replacement? If so, did you purchase this phone new directly from Apple or used from a third-party? If the latter, and you suspect that it is not the original ... and haven't purchased it yet, then don't. Or, at least, have the seller provide you with where they got it repaired and repair receipt.
Ref: About genuine iPhone displays - Apple Support