For example

val rootJob = Job()
val rootContext = Dispatchers.Default + rootJob

val otherJob = Job()
val otherScope = object : CoroutineScope {
    override val coroutineContext = rootContext + otherJob
}
otherScope.doSomethingAsync()
otherScope.doSomethingElseAsync()

rootJob.cancel() // will this cancel items from otherJob?

With this particular code, no. But normally, if you launch a coroutine in a scope with a Job, it is a child of that job. That relation isn't established when you do

rootContext + otherJob

, where the value associated with

[Job]

key is simply dropped.

So should I be checking if a

[Job]

is present and passing it as the

parent

of the

otherJob

? If I do that, will

otherJob

being cancelled cause the

rootJob

to cancel too (undesirably in my case)?

What do you want to achieve? If you explicitly use different Jobs for different coroutines there are no relationships between them, in your example above you just replace one job with another.