Who cites whom most often How can I find out which authors cite a certain author X most often?

This question is different from Influence of author on other authors because here I ask about the number of citations (a very specific metric), whereas the other question and answer are about other metrics.

(Regarding background research I tried as required by the quality standards of this site: I checked scholarly but a solution isn't obvious. Maybe following id_scholarcitedby there could work. Also, http://www.semanticscholar.org/ provides similar info (weighted influence as estimated by AI etc), but that does not perfectly correlate with the number of citations.)
John Ioannidis from Stanford has analysed citations pattern. In this 2016 paper he looks at citation patterns in multi-authorship. He commented on the impact of alphabetic authoring in the various disciplines as well.  

In a recent August study in PLoS Biology, John further explores self-citations as well. In this paper he examines "extreme self-citations and citation farms" that can skew and game the citation system. 

So yes, using his technique (he examines the Scopus and GoogleScholar database in these studies), you can probably find and examine citation patterns as well.