Not sure what you mean by "access path". Your iMovie library that contains your projects is located in the Movies folder on your Mac. The path is Go/Home/Movies from the Finder menu. If you control-click on the iMovie Library icon, and click on Show Package Contents, you will see the projects and events that are stored in your iMovie library. The items contain only data and cannot be played in the Show Package Contents view. Warning: Do not move or modify in any way the items listed in Show Package Contents, or you will risk corrupting your library. If you want to copy or move projects work within the iMovie app itself.
iMovie projects must reside in an iMovie library. Projects cannot independently be dragged to another disk unless you drag the entire library to the disk. Projects can be copied from one library to another by opening the two libraries in iMovie and then clicking on the Projects tab at the top of the iMovie screen to open the projects browser (where your projects are displayed as icons). Then move your cursor over the project title under the icon and click on the little circle with dots in it that appears to the right of the title. In the resulting drop down menu you will see an option to move or copy the project to the selected library.
This link will show you how to work with multiple libraries, including copying or moving projects from one library to another:
https://help.apple.com/imovie/mac/10.1/#/mov3fa25bae7
Your iTunes music is located in Music/iTunes (Go/Home/Music). At least it is on Mojave. I'm not using Catalina so cannot comment on where it might be located on Catalina. There shouldn't be any necessity to access your iTunes music from other than the iTunes website.
You can create an Alias by selecting the file or app's icon and clicking on File/Make Alias. Anything dragged to the dock will be an Alias.
-- Rich
