How do I ground my power supply?
Your output connector has a two-pin output connector, with +V (24 V) and -V (0 V).
See the below extract from its datasheet It states that V- is connected to AC FG, where where FG is Frame Ground.
In other words, it's stating that the -V is connected to the safety earth (ground) pin of the mains inlet. So you already have a ground connection on your output connector.

You can prove these easily enough with the fully disconnected PSU and a multimeter measuring resistance. This is common with these supplies, such as those for laptops.