Skill assessment: relevant field of study for PhD degree

Dear all,

Glad to find this forum about migration and PR application in Australia!

I am a PhD student in VIC in the field of environmental science, with research projects/publications focused on developing novel mathematically/statistical tools in land/agriculture/wildlife management. I aim at applying 190 visa upon graduation.

After browsing through many great existing posts (here and elsewhere e.g. expatforum), I noticed there is no discussion about how skill assessment authority (VETASSESS in my case) would judge the relevancy of an interdisciplinary research degree against one or more occupation ---- i.e. with a master by research or PhD degree with significant components of multiple fields of study (e.g. math + agriculture + spatial scientist), are we eligible for all those occupation?

According to VETASSESS website and migration agencies, it is not clear how applicant should prove that such a research degree is "suitable for the occupation in Australia" and has "the depth (progression) and breadth of study in the major"

My questions are:
1) How do we judge the eligibility of a PhD degree against multiple occupation?

2) What documents/subject transcripts/deliverable/prove should be prepared to demonstrate the relevancy of a PhD degree to one or more occupation?

Look forward to your comments and discussion!
I will continue searching relevant info and consult some agencies on this issue and keep this post updated.

Cheers