Shalom Rabbi, is there any Halakha forbidding from seeing or holding Bris when urinating?
There is a halacha that one should not touch his himself even while urinating because it can cause him to get stimulated. The Shulchan Aruch says that it is permitted to support oneself by the scrotum. Regarding seeing oneself at that point, although it is commendable not to do so there is no prohibition in doing so.
Shabbos 118b, Shulchan Aruch Orach Chaim 4-14, Even Haezer 23-4. See Orah Chaim 4-14, 15, 16 and Mishna Berura for more details.