When you create an asset from a subnet, only the contents of that subnet gets stored inside the asset. So if the subnet is referencing nodes outside of the subnet, those nodes likely won't be available when you instantiate your asset (for example, in a new scene), and your asset might not behave properly. That's what the warning message is about.
The /FLUID_ATTRIBS ones can be ignored. The ones that you want to take care of are: /shop/fireball and /obj/grid_object1
/shop/fireball is a shader that's created in /shop by the shelf tool. And it's being used as a shader in /obj/subnet1/import_pyro_build. Typically, you would move this shader inside /obj/subnet1 by creating a SHOP Network inside /obj/subnet1.
/obj/grid_object1 looks like a collision object that you've setup. This seems to be used by a RBD simulation inside /obj/subnet1. If the RBD simulation is part of the asset, you would want to move the grid inside /obj/subnet1 as well.
Hope that helps!