Add C wire for Thermostat to Goodman furnace
You should be able to connect to any of the blue wires, or to the chassis where the transformer is bonded. I wouldn't use the HUM  terminal, unless you've looked at the schematic and determined that it's connected directly to the transformer. If you include the model number, or a photo of the schematic.  We'd be able to tell you for sure.

If you're supplying an A/C unit contactor, the furnace circuit board, and an exhaust fan from this transformer. You may find that it doesn't have the power to also supply a thermostat. There may be no problem at all, but it's something to be aware of.