Question markers

[Ippikiryu]

I know you can use か and の (And even かい) for questions, but I've never found any explanation on when a certain is more fitting than another.

 

[Ignis]

While か is likely the most common question marker you'll find if you take a course or formal study, it's only most suitable in formal speech.

チャックノリスと呼ばれる方を知っていますか？ Do you know the person named Chuck Norris?
昨夜の流星雨を見たんですか？ Did you see the meteor shower last night?

However, it's more common to have no question marker at the end of a colloquial sentence than using か. か being there often has a rough meaning and may denote a sarcastic or rhetorical question. It has a similar nature to the use of かよ at the end of a colloquial sentence which often isn't only informal but also impolite.

彼女の人のこと知ってる？ vs 彼女のこと知ってるか（よ）？
Do you know her? vs What do you know about her!?

Admittedly, as with most other aspects of the language, the difference isn't as prominent nowadays. Nevertheless, coupled with certain verbs and context, using か as a question marker in a colloquial sentence is quite risky and something you should be careful with. This is why you often see の being used instead, although using か after の still poses the same risk.

That being said, using か at the end of an interrogative sentence in which the verb used is negative (often a volitional sentence) seems less risky.

烏賊食べないか？ Wanna eat squid?

The use of かい as a question marker seems to be favoured more by elder people and not so much (if at all) by youngsters, which is why I agree with those saying that it somewhat denotes the superiority of the speaker. Some consider it a condescending expression to use in a conversation between people of the same level (like you and your friends).

Spoken conversations, however, are very convenient - you can eliminate any and all question markers and rely on pitch instead. Unless you use the wrong tone, it should also help reduce the aforementioned risk of using か in a colloquial sentence.

 

[Ippikiryu]

Thanks, that was a great explanation! So ka and no are generally very interchangeable, but no is almost 'softer?' And better yet it to just drop it completely when possible?

 

[Ignis]

ka and no are generally very interchangeable

Umm not quite. tl;dr version:

Formal speech - use か.
Informal speech - use の or use nothing, か isn't preferred.

no is almost 'softer?'

Than か, yes.

And better yet it to just drop it completely when possible?

"More common"; I can't say with 100% certainty that it's "better".