Bob, to turn the VFD on/off using a "remote" switch, you just need to short terminal DI1 to COM. In the page "2.2.1 Typical System Connection" wiring diagram, it shows this switch labeled "Forward Run". If you connect a standard switch (like a household light switch) to those terminals, it should turn the motor on/off when you flip the switch on/off.
Perhaps this is obvious, but it's important to note that this switch is only controlling a low-voltage signal to tell the VFD what to do. It's not switching either the 240V input or the 3phase output, directly.
I would recommend getting a regular SPST switch (like a household light switch) and hooking it up and making sure it works before you get into the trouble of figuring out how to hook up the buttons from the DJ-20 (because the DJ-20 buttons are momentary, there is some additional complexity to making it work).
If you hook up the light switch and it doesn't work, I believe the 2.2.1 figure is saying that you need to adjust menu parameter F4-00 to be "1" to enable the external "Forward Run" input. By default, it may not be enabled.
Once you get that working with a simple switch, here's how to wire up the pushbuttons. Note that I "flipped" the start/stop button positions left/right from your starter wiring diagram to make the wiring connections less messy on paper
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