Hi
This is already a fairly popular question. The universal answer for him: if Celica successfully develops as a magician, as a friend and participates in all major events, then the only condition for the appearance of the second hot stone is sleep. That is, you just need to visit the Lion Temple the next morning.
If this does not work, it means that one of the participants in the next plot-important event is blocked by an unfinished quest or a low level of relations.
These things usually help: a fortune teller (relations, tresors), a bartender (quests), hints on a map (quests). As well as information about the game mechanics in the library.