"mount -t TYPE /" - how to know that what could the "TYPE" be?

This should work for ubuntu as well as Debian, type the following:

cat /proc/filesystems

This will output what your current kernel supports

ah now i understand your question better, type:

 man mount

and scroll down to -t and there will be a list of supported filesystems that mount it self supports, but this is dependent on what your kernal supports