"How does one say that in Esperanto?"
Translation:Kiel oni diras tion en Esperanto?
"tio" is a pronoun (like German "das" with one S) and "ke" is a conjunction (like German "dass" with two S).
Since you also know some French and Spanish, "ke" is similar to "que" in those languages in its use as a conjunction.
How does one respond to this question? Here's my guess, am I wrong?
Oni diras tion tiel <la frazo>