Member for 4 years, 7 months
Last seen more than a month ago
Seoul, South Korea
Yes, it is natural. 한국에 두 번째로 갔을 때, or 두 번째로 한국에 갔을 때 When you use ordinal numbers, you should put space between number(첫, 두, ...) and '번째' like 첫 번째, 두 번째.
As @Yonggoo Noh said, 확실치 is equal to 확실하지. 확실친 is a short expression of 확실치는 or 확실하지는. 확실하지는 has the same meaning as 확실하지, but those have a slight different shade of meaning. Let me explain more ...
Most of Korean can't read 漢文(the sentence written in 漢字) naturally. We know some of 漢字, but only characters because many Korean words are from 漢字. I think many young Korean know only a few 漢字, and ...