for me what I do, depends on what it is that Im not supposed to know about...

sometimes I go to the source and say I heard about such and such and heres what Im thinking

sometimes I let the issue slide and consider that I cant control what ever it is, and that my anger may be just that no one told me. Im not expected to know everything about everyone elses life or everything that does not directly relate to me.

its a pick your battles thing for me. so for most situations where I may not know something then find out accidentally I just handle my own emotions like I do with any other time I have gotten angry ....breathe and do something comforting to me. and let the big secret I wasnt meant to know about work itself out.