Is there any way to prove another player's role?

New Town of Salem Roles! :D

The existing answer gives quite a bit of information already. There have been some new roles so here are a few more specifications:

The Consigliere (Mafia Support) can retrieve the exact role of a player. However, if that person has been doused by an Arsonist, they will appear as an Arsonist as well. If the player has been hexed by a Hex Master, they will appear as a Hex Master as well.

The Sheriff can also tell if someone is part of the Coven (which is a new addition). The Investigator sees a list of possible roles of the player, and if they were framed, they will appear as Framer, Vampire, Jester, or Hex Master.

The Mayor can reveal themselves during the day which is absolute proof that the player is a Mayor.

The Witch and the Coven Leader will see the exact role of the person they choose to control that night.

There are a few ways to find the role of a person. If a Jailor jails a player and is not visited by any players, then dies to a Serial Killer or a Werewolf (on a full moon night), then the jailed player is obviously that role. If a Jailor tries to execute a player or only one player voted guilty for a Jester but they didn't die, then they have to be Pestilence, the only player with an Invincible defense.

The Consigliere is the only role that can find out for sure what another player's role is. Unfortunately for the town, the Consigliere works for the Mafia.

The Sheriff can tell for sure if a player is a Serial Killer or if they're a member of the Mafia (except the Godfather). If a player is being framed, they will appear as suspicious, just like a Mafia member.

The Investigator can tell a small selection of roles that a player might be. If a player is being framed, they will appear to be a Framer or Forger.