Can you explain a bit more about how Jupiter is involved in this? During my search I got the impression that this wasn't a favorable placement in my chart?
The "unfavorable" part is that it's in detriment. Planets are in fall when they're in the sign opposite the sign they rule and detriment when they're in the sign opposite the sign where they're exalted. Jupiter is exalted in Cancer. Expansive Jupiter loves the nurturing, sensitive "mother" sign. But Capricorn is a constrictive sign. Goal oriented, good at self denial when it seems necessary, focused. Jupiter's expansive energy doesn't shine there.
But when a planet is in the last degree of its sign--and it looks like your Jupiter is around the last minute of the last degree, right smack about to transit to Aquarius--it's excited, revved up, can't quite decide whether it's one sign or the other. That puts some more oomph in it. And planets function even in detriment. Sometimes they function better by functioning poorly, because a planet in detriment (or fall) is a planet you have to put extra effort into.
Jupiter rules education in general, and in your case, rules your career as well. Maybe you had to fight to get as much education as you did. Maybe there were obstacles to overcome. Or maybe you were simply very focused, and persevered until you had your Phd. That's a Jupiter in Capricorn gift.
Your Jupiter is a cusp planet in another way: both of the house systems you cast your chart in put it at the cusp of the eighth house. In Placidus, it's just inside the eighth. In whole sign, it's still in the seventh, but barely. Jupiter carries the message of both houses, I would say, especially where they overlap.
The seventh house is one-on-one relationships. In addition to the usual meanings of partnership, spouse, etc., it also represents your clients, if you do a kind of work that involves one-on-one client interactions. And anyone whose client you are in that kind of one-on-one work: your therapist if you have one, your doctor, your accountant, your astrologer, etc.
Placements in the seventh house that relate to career might suggest doing one-on-one client work. The eighth, meanwhile, is the emotional and energetic underpinnings of that one-on-one relationship. Psychology. The transpersonal. In a personal partnership or marriage, we're also looking at shared finances and the sexual dynamic in the eighth house.
So, you started with the seventh house part, and now you're transitioning to the eighth house part: the social structure underneath. Fittingly for your Aquarius sun in the eighth, you're interested in the psychology of the social whole.
Sun also plays some part in the profession we choose. Eighth house sun has a particular bent for doing helping work. Psychologist is a common career choice. Aquarius, though, would like to work for the greater whole, and revolutionize things. That's what Aquarius is all about.
Pisces, too, is a "greater whole" sign. One with everything. Everything interconnected. Very big picture.