We're trying to design a job ad and I'm struggling with it. The job is something like a full stack developer and data scientist who will be working as a tool smith for an analyst team.
Where should I ask for advice on how to design a job ad?
I'm afraid the scope of your question is too limited to be of general value, and most Stack Exchange sites that in one way or another deal with this topic will close it. A question about advice to design a job ad for an IT position in general, while more generally applicable, could be too broad. In general, asking for advice is a rather tricky topic, as it often leads to opinion-based answers. The Stack Exchange Q&A format works better with objective answers.
For example, User Experience has questions about advertisements, but is more focused towards how ads in general integrate with the rest of a website or app. They close review questions as off-topic precisely because of their limited usefulness for the general public.