Without a natural magnetic field and with such a slow rotation rate, the “equator” is the grayline and the “poles” are the substellar point and its corresponding antipode.

Some related notes on vulpithecine mathematics: Angles don’t use degrees but duodecimal fractions of a full circle (tau). Historically, yinrih had no words for ‘north’ and ‘south’ but only ‘toward the equator’ and ‘away from the equator’. This is still the case in at least Commonthroat. Hearthsider, being the language spoken on the planet pictured, likely uses ‘sunward’ and such.

Travelers who get lost in the Nightless Desert surrounding the substellar point are told to measure the elevation of the sun, which will tell them their latitude. Alternatively, that their shadow points to the green belt surrounding the terminator. Practically though, your best bet if you get lost out there is to either look for one of the many monasteries dotted across the desert, or failing that, find and sever a long-haul data cable and wait for the repair crew.