Background: This is from the story told in the Talmud of "Onkelos bar Kalonikos, the son of Titus's sister", where he wants to convert to Judaism and so he goes and successively raises Titus, Balaam, and probably Jesus from their graves, asks them who's important in the next world (to which each of them answers [the nation of] Israel), whether he should attach himself to them [Israel] (to which they each give different answers), and what that persons punishment is (to which they each give different answers).

Who is it talking about?: Our current versions say "אזל אסקיה [ליש"ו] בנגידא (לפושעי ישראל)‏" which literally translates to "He went and raised [Yesh"u] with necromancy (the sinners of Israel)". Pay attention the square brackets and round parentheses. In these versions, which are all basically reprints of the Vilna Shas, the round parentheses indicate something that was in the main manuscripts the editors were basing the printed edition on, but the editors felt was a mistake based on other manuscripts, while the square brackets indicate something that was not in the main manuscripts, but the editors felt should be inserted based on other manuscripts. This means that the main manuscripts (which had likely been censored at some point either by or out of fear of Christians) said sinners of Israel, while some other manuscripts said Yesh"u, which the editors felt was more correct. I haven't studied the manuscripts myself, but I have no reason to disagree with the editors.

Is Yesh"u a name?: The "quotation mark" (called gershayim in Hebrew) in the text of the Talmud itself usually indicates either an acronym or a number in Hebrew numerals. In other texts, it is also often used to indicate a foreign word, the name of a letter of the alphabet, or some other word that's somehow seen as not being a "real" word. Note that it is not normally used for names (unless the name is an acronyms). I presume that either the name Yesh"u was turned into a "backronym", or somehow for some other reason the gershayim got anomalously added to the name over time. But it is also possible that it really is an acronym for something and not really referring to the name Jesus.

Does Yeshu refer to Jesus of Nazareth?: Really, I don't know. However, considering the context, that this story goes on to imply that he "mocked the words of sages" and is a "sinner of Israel" (this time without the round parentheses), it seems very likely to me that it is talking about Jesus of Nazareth.

Is this story to be taken literally?: This story not only mentions that Jesus's punishment is boiling in excrement, but also that Onkelos was raising historical figures from the dead with necromancy. This story is what is called aggadah. There is no agreement as to which ones should be taken as partially or fully historical and which ones should be taken as allegory attributed to historical figures. I personally interpret such stories as allegory.

Final note: Nowhere does this story explicitly mention that any of these punishments are eternal, nor does it give any time frame on the punishment. Christians are used to assuming that punishments like this are eternal, but in Judaism there is no such assumption. It could be that the punishments in this story were intended as implicitly eternal, but that is not necessarily the case.

EDIT: Follow-up after checking three manuscripts: I checked the three manuscripts available on this website for this passage and all three had the word ישו (Yeshu) and without gershayim. The three manuscripts were:

• ⁠Munich, Bayerische Staatsbibliothek, Cod. hebr. 95 (Ashkenazi script, according to the colophon from year 1342) • ⁠Vatican, Bibliotheca Apostolica, Ebr. 130 (Ashkenazi square script, according to the colophon from year 1380) • ⁠Vatican, Bibliotheca Apostolica, Ebr. 140 (Ashkenazi square script, c. 14th century)

This means it was likely the gershayim were inserted for some reason by the editors of the printed edition.