"심심할때 마다 볼까?" => "심심할 때마다 볼까?" (corrected spacing)
=> Shall (I / we) see (it) whenever I am [we are] bored?
(It is a fragment of a sentence with no subject or object, so may be interpreted in multiple ways)
- 심심하다: be bored; have nothing to do.
- 심심할 때: when I am bored. 심심할 때마다: whenever [every time] I am bored.
- 볼까?: can mean "shall I/we see (it)?" or "is (someone) seeing (it)?". The former is more likely here.
* 마다: a particle(조사) for "every instance", in time, things, or people.
- 일요일마다 교회에 가: I go to church every Sunday. (time)
- 그 사람은 하는 일마다 실패했다: He failed at everything he tried his hands on. (thing)
- 지나가는 사람마다 외투를 입었더: Every passing person is in overcoat. (people)