Odd, not sure why that's failing for you. You can bypass the wget command by downloading that file in Safari, then doing

    mount -t ios . /mnt
    # Pick "Downloads" from "On My iPad" in the GUI

Then you can run

    tar xvzf /mnt/apk-tools-static-2.10.5-r1.apk

When you cd to the root.

Though, I suspect apk itself will fail if you can't resolve domain names.

Edit: As gorkish points out, make sure iSH has network permissions first and try again with the original command.