1.What does the "ὑπὸ" mean here?
It means "by" here, and is used with passive verbs like διδαχθῶ to express agent.
2. Here, does πῶς either mean "How am I..." or "How do I..."?
The answer lies not in πῶς, but in διδαχθῶ, which is deliberative
subjunctive: "How am I to be taught." If it were "How do I teach," it would be πῶς διδάσκω, wouldn't it? Note that διδαχθῶ is formed on the aorist passive stem of διδάσκω (ἐδιδάχθην).
μόνη: feminine singular
nominative, must therefore modify the
subject of διδαχθῶ.
ἀγαγόντος: Notice that this is an
aorist participle, not a present participle. The aorist participle always expresses action
prior to the action of the main verb. "Who has never led (= conducted)."
οὐδὲ ποτέ = "never once" (literally "not even ever")
θυσίᾱς: plural. And there's no "this" there.
I think you'd do much better with real Greek, JM, rather than these artificial sentences.