If you have a LUKS-encrypted partition on another disk, it's easy to mount it inside WSL.

List your disks:

> wmic diskdrive list brief

Mount the whole disk inside WSL (using --bare so WSL doesn't attempt to mount it automatically):

> wsl --mount \\.\PHYSICALDRIVE1 --bare

Now inside WSL, check the device name of the mounted disk (something like /dev/sd*):

$ dmesg | tail

Open the LUKS device (it'll prompt for your passphrase):

$ sudo cryptsetup luksOpen /dev/sdd3 my-encrypted-disk

And mount it somewhere:

$ sudo mount /dev/mapper/my-encrypted-disk /somewhere

Avoid mounting on /mnt because that's usually used by WSL itself to mount your C: drive.