According to this website (http://www.jlptsensei.com/grammar-lesson/kotoka/) "ことか is used to place strong emphasis on something." This is the only explanation I could find. I was wondering if that is a common expression and in what context would you use it? Thank you.
The ことか is used in an exclamatory sentence (感嘆文) , usually preceded by an interrogative word such as どんなに, どれほど, なんと, 何度 etc.
- どんなにうれしいことか！ (≂ どんなにうれしいだろう！)
How happy I would be!
- なんと美しいことか！ (≂ なんと美しいのだろう！ / なんて美しいんだろう！)
How beautiful it is!
- 何度失敗したことか！ (≂ 何度失敗しただろう！)
(I have no idea) How many times I have failed!
(「～～ことか！」 sounds a bit more literary than 「～～だろう！」)