Is there a way to see the sum total of all citations of all the publications of one researcher? Or do I have to go into each item and add the citations up?
I guess you found that the first page of each profile of ResearchGate members display the total number of citations. However, please note that this is the real number of citations only in rare cases. No platform is complete with regard to citations. See also these discussions:
Okay Susanne Noll great question what is the answer you found? Wolfgang R. Dick as usual very very thorough, but that is a heck of a lot of reading. I must admit either I am too lazy or just plain intimidated. I note that Google scholar profiles are listed. That would have been my answer since a diligent researcher can add papers to their profile manually as well as automatically and once entered any citations in Scholar's database to that article are counted. It is not perfect but there is no cost to the author so...