Where do I find out if a weapon has a Rune Slot

[Grcles de Cross]

I was thinking about creating a javelin with a Returning Rune on it, but I was told that this weapon does not have a rune slot. How do I find out what weapons have slots and what kind or runes can be placed on them?

Thanks

[Squiggit]

From the CRB:

Runes p.580 wrote:

The number of property runes a weapon or armor can have is equal to the value of its potency rune. A +1 weapon can have one property rune, but it could hold another if the +1 weapon potency rune were upgraded to a +2 weapon potency rune. Since the striking and resilient runes are fundamental runes, they don’t count against this limit.

As for what kind of runes, that depends on the rune itself, specific runes have restrictions on what they can be put on or not.

[Ice Titan]

Javelins aren't ammunition, so they should be able to be made +1 to gain the ability to add a property rune.

[Darksol the Painbringer]

I imagine they were told they couldn't because you cannot put runes on non-magical weapons (i.e. weapons without fundamental runes of any kind).