"To je František?"

Translation: Is that František?

[EyesOFRa]

Should it say "On" instead of "To"?

[endless_sleeper]

To je František? = 'Is that František?'
On je František? = 'Is he František?'

[shamsankar]

Because Frantisek is masculine, can it also be "Ten je Frantisek?"

[kacenka9]

No. Not really. You could only use TEN in such a sentence if you were to choose from 3 men which one is Frantisek. In such a case you could say both TO JE and TEN JE but as a reply to WHAT is it... it would always be TO. As a reply to WHICH is it. you can say TEN.