Quick recap from official sources (RROP, TDA)
show full winning hand: there's no doubt the whole hand must be shown. RROP: "A player must show all cards in the hand face-up on the table to win any part of the pot." TDA: "Proper tabling is both 1) turning all cards face up on the table and 2) allowing the dealer and players to read the hand clearly. “All cards” means both hole cards in hold’em, all 4 hole cards in Omaha, all 7 cards in 7-stud, etc."
who shows first: By RROP and TDA it's last aggressor in the final street, or else first actor in a normal round (i.e. first seat left of the button in flop games, high hand showing in stud, low hand in razz, etc.))
asking to see a hand: now RROP and TDA differ
- RROP - The Showdown :
5. Any player who has been dealt in may request to see any hand that has been called, even if the opponent's hand or the winning hand has been mucked
(with further caveats not to abuse this rule). // This was enforced in the 2005-2015 decade, but was contested afterward.
- TDA is quite precise on this topic. Per oct-2024 edition:
18: Asking to See a Hand
A: Players not still in possession of cards at showdown, or who have mucked their cards face down without tabling, lose any rights or privileges to ask to see any hand.
B: If there was a river bet, any caller has an inalienable right to have the last aggressor’s hand tabled on request (“the hand they paid to see”) provided the caller tabled or retains his or her cards. TDs discretion governs all other requests such as to see the hand of another caller, or if there was no river bet.