The above information for Isilisinisusurpa is correct to start.
You say, 'Hail, Noble Sivrn'
Noble Sivrn smiles, 'It is a pleasure to see you once again, _____.'
You say, 'Where is Isilisinisusurpa?'
Noble Sivrn says 'What you seek is beyond my ability to find. Is it not known that Rohtrepoten imparts all knowledge to those who are to be confused?'
You say, 'Hail, Rohtrepoten'
Rohtrepoten says 'Greetings, _____.'
You say, 'Where is Isilisinisusurpa ?'
Rohtrepoten says 'Foolish words fall upon my ears, backwards and forwards through the years, spoken one way is ever contrite, and the other while correct, not quite.'
You say, '?aprususinisilisI si erehW'
Rohtrepoten says 'You have everything backwards, which is the first step, betwixt twin spires forgotten games Isilisinisusurpa's kep. Playing for ages forgotten in dust, watching forever as all falls to rust. You will not see the hidden without seeing them first.'
In the vicinity of 1125, 700 is what appears to be an abandoned game board (which conveniently lies betwixt twin spires). Walking over the stone "squares" causes the appearance of some to change slightly... This is where Isilisinisusurpa is believed to be. (More information needed.)
from here - if you stand in the middle square (the loc above 1125, 700) of the row of squares between the two pillars facing north and say 'Where is Isilisinsusurpa?' the sphinx will appear not to far away north of you.
You say, 'Hail, Isilisinisusurpa'
You have been assigned the task 'The Hidden Sphinx'.
Isilisinisusurpa says 'I am a carefully constructed facade. Irresistable and impenetrable. All but invisible. You see me through the disturbance I create. That which i displace shows my form, but nothing more.'
you are assigned a task named The Hidden Sphinx, and it is one step - pronounce the name of Isilisinisusurpa correctly (8 syllables) and the help text at the bottom says to say it to Noble Svirn. i unfortunately didn't get a screenshot. said 'I`sil`is`in`is`u`sur`pa' to Noble svirn and it completed with an exp message and noble svirn emoting "Noble Svirn nods in approval."
i do not know if it matters any - but i put up see invis as well prior to going to the game board as rohtrepoten said you will not see the hidden without seeing them first - just took that to be need see invis.