The process to transfer content from one Google account to another can be a bit complicated or it can be simple. It all depends on what types of content you have and what you expect to do with that content when you're done. You may also just need to download it for future reference. That said, here are a few tips.
When you use the Google Drive for desktop client app (formerly Google Drive File Stream) on your computer, it syncs all of your content from Google Drive to a mapped drive on your computer. This allows you to use Windows Explorer on a Windows computer or the Finder app on MacOS to then copy the files from that mapped drive over to your computer. From there, you can upload them to another Google account (or just leave them on your computer).
This method works great if the files you need are not Google Docs, Google Sheets, etc. So if you're downloading Microsoft Office documents (Word, Excel, etc), PDF documents, images, etc, you'll easily be able to open those files in other apps after you've copied them.
Google provides a service called Takeout, which allows you to export a copy of your account and back it up. You start by selecting which content to download (calendar, email, drive, etc) and then follow their prompts. You will end up with an archive file on your computer.
At this point, some users will then wonder what next? It's a good question which is not easily answered. Google does not provide a simple way to then import that data somewhere else. You'll need to consult documentation for the app you want to use for help on how to import it.
This is a good option if you're just not sure what you'll do with the content next, and you want to be sure you have a backup copy of all of your content to save indefinitely.
More details are available in this article:
Transfer Your Content
As part of their Takeout product, Google has a function which allows you to transfer your content. This is ideal for transferring content from your SNC account to another Google account. Please note that we're not able to do this for you, nor are we able to assist with the import or use of that content on another account. As the owner of the two accounts, you'll have to do this.
Just follow the information provided by Google in their article:
As a last resort, you can always download content manually. In Google Drive, you can right-click on a file and select "download". In Gmail, you can open a message and forward it to another email address, or just select "print" and save it as a PDF. This process can quickly become tedious, but perhaps it serves as a last resort if you just need a quick way to save something.