A few things.
First you should almost never sudo su. There's no reason for it, but lets pretend your in one of the very few circumstances where you want to sudo su.
sudo su (no
-) will keep you in your current directory and bring over your current shell setup (i.e. vars and such). So your real answer is to use
sudo su without a
-. Now lets pretend you want to use it together with
- for some reason (note: the usages for this are damn rare). The result is that you will log in as root and not just run things as root.
Third, assuming you want to get back to your directory after
sudo su -ing. Your best bet is to just copy and paste, or navigate back to the directory. However, if you insist:
sudo su - -c "cd `pwd`; bash"
I would like to stress however that you are almost certainly using sudo and su incorrectly. The whole point of sudo (and not having a root account) is so that you run things as your self with elevated permissions. Your circumventing that.
I suggest reading: