What pronunciation to use ? Kun or on-yomi?
In that particular story it’s being used in the word "休暇”(きょうか) so it’s using the on-yomi reading. (か)
No. They’re asking about the kanji 貯, not 休 or 暇. Also 休暇 is read as きゅうか not きょうか.
It looks like it’s being used in the phrase “お金を貯め” which is read as the kunyomi た （part of the verb ためる, to save)
The kunyomi is usually used when there is okurigana as a rule of thumb.