Extended version of Blade[UG]'s answer because I was already typing it...
What do you mean by this? I assume in your defaultproperties? When referring to assets in code you use the following format:
Originally Posted by lukesmith
Or an actual example:
This means the asset is a static mesh named S_Ammo_ShockRifle located in the Ammo_Shock group of the Pickups package. You need to use this same format for your own content. An easy way to get the reference is to copy it from the Content Browser by right-clicking on the asset and choosing Copy Full name to Clipboard. Then just paste that into your code.
The folder the package is in is irrelevant other than needing to be in the Content folder at the very least.