Summary: Duolingo probably ought to accept confirm, verify, establish, or check for this one.
Details: I first checked the Harper-Collins bilingual dictionary.
Collins has a nice example: "Pudimos comprobar que era verdad" which they translate as "we were able to verify/confirm/establish that it was true."
Comprobar can also mean "check" as in "check your oil/passport"
And it can mean "prove" as in math.
Looking at the Diccionario de la Lengua Española (the OED of Spanish), it defines comprobar as "Verificar, confirmar, la veracidad o exactitud de algo." It makes no real distinction between "verify" and "confirm" in this sense. Confirmar can also mean "revalidar," which includes the notion of double-checking something, but that's just one of eight things it can mean, and definitely not what comprobar means.
I think English and Spanish have the same ambiguity over whether this means to verify the exact words you said "I can confirm that he said the Earth is flat." or verify the truth of what you said.
Hope that helps.
lo que = that which / what
que = that
¿Qué? = What?
"He showed me what was lacking." Is that, "He showed me that was lacking"? No. "He showed me that which was lacking"? Yes! So it is, "Me mostró lo que faltaba."
"He showed me that we were lacking five apples." Is that "He showed me that which we were lacking five apples"? No. So it is, "Me mostró que nos faltaban cinco manzanas."
"What are we lacking?" "¿Qué nos falta?"
She definitely pronounced pueden as pueben. I didn't fall for it though. A problem I've noticed when listening to natives speak is that they sometimes have sloppy pronunciation. They mumble. I used to think that this was the correct way to speak, and worry that I would never be able to match this perfection. Now I just view it as sloppy and incorrect and liken it to the English spoken by Rab C Nesbit. I know the D is meant to sound soft here but that was definitely a B sound.
They are very close in meaning, and I suspect your Spanish friend doesn't grasp this.
"Verify" is more typically about action(s) one takes that involves gathering outside knowledge to validate; "confirm" is generally broader, drawing upon one's own or outside knowledge to validate. But given the scope of definitions they each have, they are very nearly interchangeable.
I don't know if "comprobar" has a narrower definition that accounts for only some of what "verify" and "confirm" can capture. It would be interesting to hear from a native Spanish speaker with a good grasp, or an RAE consult.