XMonad doesn't provide any system tray facility so for apps that require one you will need to install a system tray app like Trayer and add that to your .xSession or similar startup file. There are a lots of examples of how to set up a tray with XMonad, usually with some sort of panel. I use XMonad.Layout.Monitor to float a transparent xclock and tray in the top right corner of my screen. Note that I have used a fixed position and size for simplicity, you may want something more dynamic.
trayer = monitor { prop = ClassName "trayer", rect = Rectangle (1920-150) 0 100 16 -- avoid flickering, persistent = True -- make the window transparent, opacity = 0.6 -- assign it a name to be able to toggle it independently of others, name = "trayer" } clock = monitor { prop = Title "clock", rect = Rectangle (1920-50) 0 50 16 -- avoid flickering, persistent = True -- make the window transparent, opacity = 0.6 -- assign it a name to be able to toggle it independently of others, name = "clock" } myLayout = ModifiedLayout trayer $ ModifiedLayout clock $ layoutHook defaultConfig