"I typed "ji" and was told it was incorrect.
It is. There's a difference between JI and JÍ.
"jí" is genitive while "ji" accusative, right? I was sure that accusative was needed in this case...
Vážit si někoho/něčeho requires genitive. The full declension is here https://en.wiktionary.org/wiki/ona#Declension
And "Tú si jí vážíš?", can that work?
Ty si jí vážíš? is ok. Such a sentence suggests a certain element of surprise (emphasis on vážíš).
And I image it is quite confidential. Thank you Endless for the many advices.
"Její si vážíte?" Is not accepted. Is it possible?
Její is a possesive pronoun, not form of "ona" https://en.wiktionary.org/wiki/ona#Declension
Could I ask anybody why "í" in "jí" sounds so short here?
I can't hear such a thing. But I disabled the new male voice because it has problems with the first words.