In a recent D&D 5e session, the issue came up where the party wanted to identify an undead creature, along with its strengths and weaknesses.
The party Wizard wanted to use the skill he was proficient in (Intelligence (Arcana)) since according to the PHB it covers "... the planes of existence, and the inhabitants of those planes".
The party Paladin wanted to identify it using the skill he was proficient in (Intelligence (Religion)). Although undead are not explicitly mentioned in the description of that skill, his logic was that learning about undead and their strengths and weaknesses would make up a significant part of his religious training as a Paladin.
Is there a (RAW) explanation of which skill would give a player insight into the nature of undead enemies? Is it either of the mentioned skills, or more based on a character's background learning, as decided by the GM?