I don't think that's going to work, unless he has enabled a root password -- not the default in an Ubuntu installation.
What should work is this:
$ sudo su
# whereis dpkg
Since both my SimplyMEPIS 3.3.2 & 6.0 systems show
I have every reason to believe that that's the right answer for Ubuntu also.
sudo dpkg --configure -a
-- I don't think sudo
needs the quotes.
Also, would you please post (by pasting) your key commands & error msgs.?