Aid Another skill check qualification

[IQuarent]

In order to Aid Another with a trained-only skill such as Disable Device, do I need to have ranks in the skill or is having it on my list of class skills enough?

[Rennaivx]

Second paragraph of your link wrote:

...you can't aid another to grant a bonus to a task that your character couldn't achieve alone.

So no, you can't assist a trained-only skill without training, since you wouldn't be able to do it on your own.

[Drejk]

Aiding another requires appropriate skill check by the character providing aid. Without actual training that character can't make a skill check of a trained-only skill check.

[Jeff Merola]

Not to mention that for trained-only skills you have to be able to actually achieve the task in question to aid. For an example, if you only have a +4 Disable Device check, you can't actually aid in a check to pick a DC 30 lock, since that's a task you "couldn't achieve alone."

[Just a Guess]

The problem with aiding for skill checks is: Many times the aider would be better off trying it for himself.
How often do you have the following:
pc1: I'll go hunting
pc2: I aid him
pc1: *rolls* I have a 12 on survival
pc2: *rolls* I have a 19 so you get the +2 bonus for a total of 14.