I am not sure there is such a way that you can "automatically" find your highest cited publication in ResearchGate. In fact, ResearchGate website does not support sorting publications by the number of citations like the other databases such as Web of Science, Scopus, Google Scholar....etc. Therefore, you can use these previously mentioned websites to find your highest cited publication, then you might go back to ResearchGate and manually save it in the "Saved List" of ResearchGate to print it later.
I am not sure there is such a way that you can "automatically" find your highest cited publication in ResearchGate. In fact, ResearchGate website does not support sorting publications by the number of citations like the other databases such as Web of Science, Scopus, Google Scholar....etc. Therefore, you can use these previously mentioned websites to find your highest cited publication, then you might go back to ResearchGate and manually save it in the "Saved List" of ResearchGate to print it later.
Usually number of citations in RG is not considered by all of academic institutes. Instead, you can go to Scopus website, authors and write your name then click on citations.
This option is yet to be included in ResearchGate. It is not possible to sort the list of publications by number of citations. However, this feature is available in Scopus and Google scholar database. Please refer the attachment.
Look at the reply of Mohammed O. Al-Amr on december 24th. If you go to "scores" on your profile page you find the button "see more" and here you can see the list ranked on number of citations. Thanks Mohammed I didn't knew this, great tip!