What is this question asking?

[Vulcan879]

いつ着くの？

I don't understand the role of the 'no' particle in this sentence. So far far I've understood it to specify the the type of something (sensei - koukou no sensei) or possession of something (neko - Akira no neko). So, does this mean that the question is asking what kind of "how soon to arrive" ? And would that make the answer, if I spelled it out,
"着くの四じです" ?

 

[Toritoribe]

It's not the possession particle, but a sentence final particle.
Noun-related particles - Tae Kim's Japanese grammar guide

着くのは4時です, 4時に着きます or more simply just 4時です.

 

[Vulcan879]

It's not the possession particle, but a sentence final particle.
Noun-related particles - Tae Kim's Japanese grammar guide

着くのは4時です, 4時に着きます or more simply just 4時です.

Thank you. That was much simpler than I had thought.