It seems to me that sometimes the "no" that should be between two nouns is omitted. if so, can this be done in any case or are there special cases?
For example, a case where I think there should be a "no" particle is this
Birusu-sei de shugyō kaishi da!
I translate this as "It's the training's start in Birusu's planet" (correct me if I'm wrong), and if I would have to write this back for me I would add a "no" to read
Birusu-sei de shugyō no kaishi da!
A similar phrase it's seen to use the "no"
Gokū wa shugyō no tabi he!?"
Why? Is it optional?