The italian version of the AD&D Player Handbook explicitly states that you need two separate rolls.
Pag 56 (roughly translated):
To find a trap, the thief must be able to manipulate the item which contains it. Usually the DM rolls the dice secretly...
[...]
Once found, the trap must be disarmed. This roll requires 1d10 round. If he succeed, the trap is neutralized. A failed roll means that the device is too complex for the thief, but he will be allowed to try again once he levels up. If he scores between 96 and 00, he triggers the trap immediately.
Perception is for observation, Investigation is for deduction.
Some of this answer will be observations on how Wizards has done it so far and some of this will be logic, and some of it will be mechanics.
First for the headline question. It depends. when to use Investigation, and when to use Perception is not entirely clear yet, and I'm hoping we'll get more guidance in the DMG late this year. The guidance from the rules is that the two skills mostly seem to differ in the methods by which they are found.
Depending on the exercise, either, or both of the skills may be used.
For passive checks, you're almost always looking at Perception being the skill of record. While all skills can be used passively, some skills make more sense than others. Perception is the hallmark passive skill, whereas investigation makes less sense as a passive skill.
If the character is alert to the possibility of hidden objects/traps, but not actively searching, he's using passive perception.
The guidance for this seems to be (though we can't confirm yet), that the DC for actively looking for something is regularly about 5 less than the DC for passively looking for something (or sometimes actively looking always reveals it).
So here's how I would play it. Traps can be noticed with perception passively (usually DC 15). If the PC is looking, ask them how they are looking. If it's observational, then use Perception. If it's deductive, use Investigation. When they are searching for items, again, either skill is appropriate. This is somewhat counter to how WOTC has written adventures so far. They are always written to use perception to notice traps. Passive with a higher DC and active with a lower.
Investigation also has broader uses such as when you are trying to track clues, or put something together. It's also a great "roll for a hint" kind of skill if your PCs get stuck and need some help figuring out what to do next.
Best Answer
Not exactly a skill, but there is a related feat, entitled Dungeon Delver, which gives the benefits
There is no specific skill that gives knowledge of traps and what sorts of threats they pose, though some skills, as you've noticed, may be useful. But an Arcana check, for example, might be appropriate to determine the nature of a magical trap once detected.
Beyond that sort of case, it is the DM's responsibility to decide how much a character would know, and could make them roll whatever kind of check they thought was most relevant (or, if none in particular, a skill check like Intelligence).
Some tool proficiencies might give particular expertise: proficiency with thieves' tools provides "additional insight" to Investigation and Perception checks when looking for traps; proficiency with a poisoner's kit gives "an edge when you inspect poisoned objects," proficiency with mason's tools means "you can spot irregularities in stone walls or floors," and many more possibilities.
There is no general skill associated with "knowledge of likely traps."