I’m on Arch, so my help may only be worth so much to you. I had the vice package installed on my system but hadn’t yet launched it as it didn’t have a .desktop file. I did a $ pacman -Ql vice | grep bin/ and guessed that the C64 emulator binary was /usr/bin/x64, so I ran it and it booted into Commodore 64 BASIC V2 as expected. Attaching a disk is available in the Alt menus under File (“Attach disk image”) and similar menus exist for cassettes or cartridges. Selecting one such option opens the file picker dialogue. Additionally, x64 -h lists command-line options for doing the same actions given a specified file. Have you found any of these solutions to work on Debian?
Edit: I see that you mean the kernal ROMs that are included in the vice package on Arch. The Arch package installs them to /usr/share/vice (for example, /usr/share/vice/C64/kernal-251104-04.bin).