It seems there aren't any indigenous lifeforms...
Praxis was the inhabited sole natural moon of Qo'noS. It was used as
the Klingon Empire's key energy-production facility in the 23rd
However, by 'inhabited', this seems to be referring solely to those Klingons who inhabited Praxis
Memory Beta also states that:
In 2293 over-mining and insufficient safety precautions led to the
destruction of Praxis in a massive explosion. The shockwave from the
explosion damaged Qo'noS's ozone layer, hit the USS Excelsior, and the
remains of the moon formed an asteroid belt around Qo'noS which
threatened all life on the Klingon homeworld. Klingon scientists
estimated Qo'noS would not be able to support life just thirty-four
years after the disaster and the Federation predicted the fall of the
Klingon Empire within fifty years as a result. (TOS movie &
novelization: The Undiscovered Country; TOS novel: Sarek; TOS comic:
"The Order of Things")
Note how ecological damage is referred to on Qo'noS only; surely if there were indigenous life forms on Praxis, that would have been mentioned somewhere as well.
Additionally, Memory Beta explains that in an alternate reality:
Having reached a stalemate in the five year war, the Federation felt
that deployment of the device on Praxis would act as a demonstration
of force and lead to a possible Klingon surrender. Although the moon
had a population of about 500,000, the Federation thought that since
most either lived underground or in colonies protected by shields and
domes, the inhabitants would be spared any ill-effects from the
Genesis wave as it re-formed the moon's surface.
This suggests to me that Praxis wasn't really suitable for any native life forms to survive naturally.
Memory Beta also mentions that at some point an Iconian gateway had been placed on Praxis, so possibly, whilst not native, some life forms may have arrived at Praxis prior to the Klingon arrival.