"Is it two o'clock?"
Kana really needs to be a Larger font. I cannot see the shape of the inner lines. It's like shrinking or alphabet by 3 sizes and then squashing all the letters together into the space a single letter takes.
Correct, without it, it would mean "It is 2 o'clock" as opposed to "is it 2 o'clock?"
It's the difference between the kanji (二) and katakana (ニ). They look extremely similar and it can be difficult to tell which one you are inputting if you're using a romaji predictor system (as they are both "ni"). Honestly, they should just accept both.
Pretty sure it's part of 'desu':
'Ni ji desu ka' - 'Ni' is 'two' - 'Ji' is 'hours' / 'oclock' - 'Desu' is 'is' - 'Ka' turns it into a question