Is it possible to use 好き, and specify who is fond of it?
風呂は好きです。
Would be interpreted as "[I am] fond of baths.", and
風呂は好きですか
Would be interpreted as "Are [you] fond of baths?".
How would I specify that it was someone else who was fond of something, if that's possible?
I think part of the answer to this question is in implicit/implied topics and the difference between the topic marker particle (は) and the subject/object marker particle (が).
Though it can sound clunky and unnatural in English, the Xは… can frequently be translated as "as for X, ...", "concerning X, ...", "on the topic of X, ..." etc.
Normally, who is being talked about is figured out by context, and so it can be omitted/elided:
（私は）風呂が好きです。
(As for me, I) like taking baths.（私は）風呂は好きです。
(As for me), concerning taking baths, (I) like them.
（あなたは）風呂が好きですか？
(As for you), do (you) like taking baths?（あなたは）風呂は好きですか？
(As for you), on the topic of taking baths, do (you) like them?
But (especially in places where it can't be figured out by context), you can explicitly mention who, e.g.:
田中さんは風呂が好きです。
As for Tanaka-san, he/she likes taking baths.田中さんは風呂が好きですか。
As for Tanaka-san, does he/she like taking baths?
Both 風呂は好きです and 風呂が好きです are possible, but in the case of 風呂は好きです I think I'd often expect to hear a が after it like 風呂は好きですが,… "As for taking baths, I like them, but..." or something, and I think it's more common to use 風呂が好きです if you want to say "I like taking baths".
AFAIK ～は好きです can sound more general and ～が好きです more specific, which might be why you'd generally say あなたのことが好き instead of あなたのことは好き as I think the latter can be used in contexts like "I like you (but not specifically you)" or "I like you (but there may be reservations/conditions etc)".
Context.
[Out of the blue] 風呂は好きですか
'Do you like taking a bath?'A: この犬は太郎と言います。
'This dog is called Taro' .
B: 風呂は好きですか
'Does she/he like taking a bath?'
Or explicitly say it.
次郎は風呂が好きです。
'Jiro likes taking a bath.