There were some plugins for standard particles that let you do that but without those (I don’t think they are available/work with the modern versions anymore). With TP it’s very easy, you want the PDeflector node. There are tuts available and you can do a lot just checking out the TP presets in the Content Browser – if you don’t have those they’re on Maxon’s site in the Downloads/Materials and Goodies -though from v11 onwards they should be on your install DVD. Try dropping in a TPStandard emitter and a TP Object Collision and an object to reflect off, the object has to be polygonal, and drag the object into the TP Object Collision/Collision Object attribute. Getting it to work inside an object will mean aligning the normals the right way and/or setting the PDeflector node (it’s in the the XPresso attached to the TP Object Collision) to Front Back or Two Sided. All of it can be done with a single XPresso tag if you are making it yourself and not using the presets FWIW.