So just to follow-up I ended up eventually finding parts of the answer online and getting something to work. I now have codes that work for both options:
dv.taskList((dv.current().file.tasks)
.filter(t => (t.section.subpath === "Brain Dump" || t.section.subpath === "6 Priorities") && !t.completed)
)
TASK
WHERE file = this.file
WHERE (meta(header).subpath = "Brain Dump" OR meta(header).subpath = "6 Priorities") AND !completed
Sharing in case it ends up being helpful to anyone else!