「買ったら」, the past tense of 「買う」 with 「ら」 appended, is one of the conditional forms available for use in Japanese (meaning "if" or "when"). 「よい」 is a formal way of saying 「いい」, meaning "good." So very, very literally, this sentence is asking "As for you, at what place if I buy a ticket is it good--do you know?" Does that make sense? A far more natural translation would be "Do you where where it'd be good to buy a ticket (or, tickets)?"
This kind of conditional is formed with any verb by attaching 「ら」 to the past tense form. Some examples:
たべる → たべた → たべたら
のむ → のんだ → のんだら
する → した → したら
And some example sentences:
1. 病気(びょうき)になったら、大変(たいへん)ですね。 (If I become sick, it'd be difficult.)
2. しゅくだいをなくしたら、どうしますか。 (When you lose your homework, what do you do?)
3. なにを言(い)ったらいいか、まだわからない。 (I still don't know what it would be good to say.)
I'll have to let someone else handle the 「し」 question for now. Hope this helps.