Obito can use susanoo (not PS) without kakashi. All you need is 2 Mangkyou level sharingan. Or the mastery of the ability in each eyes.
No, kakashi cannot since he wont have the 2 MS.
Should i use a scalpel for the dissection? I havent done it in awhile, im a bit rusty.
Kakashi was able to unlock a higher level of Susanoo(lets call it God Susanoo) because of Obitos chakra that resides within him (or in his eyes)
The mixture of 2 kinds of chakra turns it into EMS (other may say that obitos eye is still his, how come it acts like EMS and never goes blind? Well hes got another chakra = zetsu's)
This explains the nature of EMS. As for unlocking susanoo, it is often speculated that you will need BOTH eyes.
True but it is because of the mastery of the ability of each eye is needed to unlock the 3rd ability(when using both eyes)
Obito couldnt have been able to use the susanoo due to: low on chakra (or specializing it for dimension jumping to save sasuke) or that he still hasnt mastered it yet (straining or bleeding eyes indicate that the user has been pushing it to the limit, thus signifying that the user is not very efficient at using the eyes)
As for kakashis GS, he acquired obitos chakra in which he infused in kakashis eyes; therefore, giving him his MS.
This gives him the normal Susanoo (or NS) but since theres 2 different kinds of chakra, this turns kakashis original eyes (now MS) into EMS (PS). Obito also transferred his rykudou chakra thus giving it another boost turning his PS into GS.
As for mastery of abilities argument: kishi made a point that kakashi was the copycat ninja (Naruto saying "this is why hes called the copycat ninja"). Having mastered the left kamuii (quite recently might i add), he managed to copy the right kamuii and master it with ease.
As he has encountered the Susanoo many times, NS or PS, he has already "mastered b it but just lacked the necessary requirements to do the ability. Until now.
This conclude my kishi asspull summary
