Hey,
I am operating on an offline computer and want to know
if there is a way for downloading for example the free “Infinity Blade: Grass Lands”-pack
and transfering it to my offline workstation.
If yes, how do I do it, and where do I place the files so I can use them in UE4?
Thank 
Hi there,
Unfortunately, you will need an internet connection to download any assets on the Marketplace. The Infinity Blade content can only be obtained on the Epic Games Launcher.
If you want to get just the assets to your offline computer you can create a blank project and then Migrate the assets(right click on assets in the content browser) you like to that project’s Content folder. Then bring that project to your offline computer and again migrate those assets to your project’s Content folder.