Get yourself a profile on Google Scholar (mine is https://scholar.google.se/citations?hl=en&user=R9TtRLUAAAAJ), and then add your publications to your profile. Google will then track and display citations automatically.
In ResearchGate, open the page of the arcticle and click on "Citations". However, ths works only when there is a number in parantheses after the word "Citations". If not, RG has not yet found any citations. Note that often Google Scholar find more citations than RG. But both are very often not complete.