Multi-messenger diagnostics for core-collapse supernovae (CCSN) have been used for over half a century when astronomers began using dust grains to probe the yields from supernovae. But the concurrent neutrino and electromagnetic observations of SN 1987A, a core-collapse supernova in the Large Magellanic Cloud, cemented the importance of multi-messenger diagnostics for these transients. Although rare in the Milky Way where supernovae can be probed by multiple messengers, the science enabled in each event is enormous. Most of the gravitational energy released during collapse is emitted in MeV neutrinos that should be detectable within a few Mpc with next generation (NG) neutrino experiments. They may alsobe detected by future gravitational wave (GW) interferometers. Including dust grains (and other nucleosynthetic yield probes), cosmic rays and high-energy neutrinos that probe shocks, and abroad range of thermal and non-thermal photon emission, these messengers probe nearly all aspects of the supernova physics and its progenitor evolution. The multitude of diagnostics from anearby supernova will allow us to tightly constrain our theories to maximize what we can learn about the universe from more distant, but less-well diagnosed, supernovae.