This mantra is often encountered in the concluding section of Tibetan sadhanas.
oṃ su pra ti ṣṭha va jra ye svā hā
oṃ supratiṣṭha-vajraye svāhā
The Tibetan pronunciation is: oṃ su tra tiktha benza yi so ha
The Sanskrit words are:
supratiṣṭha = standing firm, firmly supported, well supported (from su + pra + √sthā)
- √sthā > basic verb form tiṣṭhati ‘to stand, to remain’; and tiṣṭha is then a verbal noun: ‘standing, remaining’.
- su- = a suffix meaning ‘well, good, excellent, right, virtuous, very, etc’
- pra- = an intensifying suffix: pratiṣṭha = ‘supported, firm, resistant’.
vajra = diamond/thunderbolt; Reality.
-ye = suffix for the dative case meaning to or for
I think the two words go together in a compound (of the karmadhāraya kind) i.e. supratiṣṭhavajraye (with the stress on va). This means something like “for the firmly supported diamond”.