The way I’m translating it now I have τί as a substantive, so it should read something like: “What, then, is that which the man spoke before his death?” I’m bothered, however, that ἅττα, which I think is being used as a rel. pro. without the “whatever” sense, is plural. Is this a regular usage?
Neuter plural nouns take singular verbs. ἅττα is neuter plural. I studied Greek for a year and a half or more before I realized I had overlooked this quirk. Presumably the neuter plural was originally thought of as a general idea. I’d like it better if Plato did’t use the singular τί , but it doesn’t surprise me. If you dig around in Smyth, you might find something more detailed.