The OP there asks how the Mekoshesh, the one who chopped wood on Shabbos could be put to death if he needs to be warned first, and the warning must contain the punishment, yet the passuk explicitly states that they didn’t know the punishment.
I answered, based on Sanhedrin 78b and 80b, that they did know that he was liable to death, just not which death penalty. According to the Tanna Kamma, that’s enough, and according to R’ Yehudah, it was a unique case.
But what about the Mekalel? In Vayikra 24:10ff we’re introduced to a man who blasphemed against Hashem. Similar to the woodchopper, he was thrown in prison, as the punishment wasn’t known. Also similar to the woodchopper, Sanhedrin 78b poses two explanations of the incident.
In context, the Gemara is analyzing a dispute between R’ Nechemiah and the Rabbanan regarding the Halacha that if Reuven attacks Shimon, we imprison Reuven and wait to see if Shimon recovers or not. Both agree to this Halacha, but because of technicalities beyond the scope of this question, they are forced to derive it from different sources. Further, we need a source for each where even if we don’t know whether he would be liable to the death penalty, we would still imprison him.
ורבי נחמיה יליף ממגדף דלא הוה ידע אי בר קטלא הוא וחבשוהו ורבנן מגדף הוראת שעה היתה כדתניא יודע היה משה רבינו שהמקושש במיתה שנאמר (שמות לא, יד) מחלליה מות יומת אלא לא היה יודע באיזו מיתה נהרג שנאמר (במדבר טו, לד) כי לא פורש וגו' אבל מגדף לא נאמר בו אלא לפרש להם על פי ה' שלא היה משה יודע אם הוא בן מיתה כל עיקר אם לאו
And [from where does] R’ Nechemiah [learn this]? He derives it from the blasphemer, for [Moshe] did not know if he was liable to death or not. And [why do] the Rabbanan [not learn from the blasphemer]? It was a hora’as sha’ah. As we taught in a Braisa: [First half deals with the woodchopper.] But by the blasphemer, it doesn’t say [“For it was not explained,” as it does by the woodchopper,] but rather “to explain to them by the word of Hashem,” for Moshe did not know if he was liable to death at all or not.
I understand according to the Rabbanan, this was a unique case, similar to R’ Yehudah’s understanding of the woodchopper. But according to R’ Nechemiah, how could he be killed? Whether he holds like the Tanna Kamma or R’ Yehudah, nobody knew what the appropriate punishment was, so how could proper warning be administered?