sharingan helps it's user to see through a technique. you just don't see a technique once and obtain it.
for example, kakashi was able to copy 1000 techniques because even before he obtained sharingan he could use rasengan, which is to release and concentrate chakra, and chidori an elemental technique. he already could do all those so when he saw someone using a lightning based attack he immediately learned how to do it and thus became able to use it as well.
another example is sasuke. he has seen rasengan countless times too but he can't use it. why? because he doesn't know how to release, rotate and concentrate the chakra.
when he saw naruto using the technique he immediately realized these three steps but since he doesn't know how to do those he couldn't copy the technique. in other words in order for naruto to learn the technique jiraiya had to explain the nature of the technique and even give examples. if it was sasuke, using the technique once and then saying "destroy the balloon" , "destroy the rubber thing" and finally "don't destroy the balloon." would be enough. sasuke would be able to get the rest.
that's how sharingan works. so if tobi knows about releasing, rotating and concentrating he can use rasengan. if he has experience in the field of summoning he may be able to use edo tensei as well.
