I haven't found the documented way to see the sdcard content for different users on a multi-user android nexus7 using adb (suppose I need to see some debug logs). However I did find this:
What is listed is not actually the content of /storage. There are listings for user 0 (root) and user 10 (the other user). You can confirm this with ps, you'll see processes prefixed with u0_ and u10_.
ls ../0 lists the tablet owner's files
ls ../10 lists the other user's files
You can also copy files from there.
cp ../10/Download/somefile .
Note: Even tab autocompletion works too.