If you want to create an Assets layer to store all sprites and them load them from there, to use in other layouts, you don't need that layout to have an event sheet, nor you need any special code. Just put all assets in one layout and you're done.
When you need to create an instance of anything that's there, just create it normally.
See this capx:
https://www.dropbox.com/s/s71snerwigpa7 ... .capx?dl=0
I created a layout with 3 objects: a sprite, a particle and a text. Then, from another layout, I just randomly create one of the 3 every 0.2 seconds.
Hope this helps. Cheers.