You can output a PPS signal driven by the PHC clock on the SYNC_OUT pin, which you can then measure on an external device (e.g. oscilloscope or logic analyzer).
# Configure SYNC_OUT pin for periodic output
sudo ./testptp -d /dev/ptp0 -L 0,2
# Generate pulse of width 1us every second
sudo ./testptp -d /dev/ptp0 -p 1000000000 -w 1000
The -p argument gives the time between the start of each pulse in nanoseconds;
the only acceptable values are 1000000000, meaning 1 second, and 0, meaning
to stop generating pulses.
The -w argument gives the width of the pulse in nanoseconds; the maximum value, which is
also the default, is 4095, meaning just over 4 microseconds.
The RJ45 ethernet port should have a carrier (e.g. be plugged into a switch).
If you have an oscilloscope, you can of course use that. Bear in mind that the PPS pulse width generated is much shorter than usual. (Typical PPS width from a GPS is 100ms, whereas this is 0.004ms.)
If you do not possess any suitable measuring equipment, the cheapest way to see the pulse is to use sigrok with a cheap Cypress FX2-based logic analyzer. These are available for about $10 on AliExpress: search for "USB 24MHz 8 channel logic analyzer".
The TAPR TICC looks like a good option for doing much more precise measurements, at a relatively affordable price.
Here's a photo showing a measurement using the CM5 and an inexpensive oscilloscope (an FNIRSI 5014D). Note that on the CM5 the SYNC_OUT is on pin 6 (which the silkscreen incorrectly labels as USB_OTG). This is using a pigtail (15cm SMA bulkhead female to Dupont 2.54mm female bought from AliExpress) with the Wifi antenna mounting hole on the CM5 IO board case to make the SYNC_OUT signal available outside the case.
