Praise be to Allah.
What is to be said in sujood al-sahw is the same as what is to be said in the sujood of prayer, which is to say Subhaana Rabbi al-Alaa (Glory be to my Lord Most High) or other tasbeehaat which are reported as being sunnah to say in sujood. Others duaas which are sunnah to say in sujood may also be recited.
There is no specific mention of how the tasbeeh should be said in sujood al-sahw. The author of Al-Sunan wal-Mubtadaaat said: There is no report that the Prophet (peace and blessings of Allaah be upon him) said any specific words in sujood al-sahw; the adkhaar to mentioned in sujood al-sahw are the same as those to be recited in the sujood of prayer. As regards the belief that one should say Subhaan man laa yashu wa laa yanaam (Glory be to the One Who does not forget or sleep), neither the Prophet (peace and blessings of Allaah be upon him) nor the Sahaabah did this, and there is no evidence for it in the Sunnah. (p. 74, 75). And Allaah knows best.