In brief, Retrogradation weakens Jupiter (or any other retrograde planet) exactly how that will show up (if at all) depends on Jupiter's overall dignity. Modern interpretations will see retrograde as focussing on inner rather than external issues - however that's probably a signification that they're really not sure at all what it means LOL
To evaluate Jupiter properly, you need to look at it in it's entirety. What is it's essential dignity (or debility) and what is it's accidental dignity (in addition to the angularity and retrogradation). Also what houses does Jupiter rule and how important are they in your life.
Remember that a planet can signify a variety of things (within its natural signification and the above dignities) and, within a natal chart, these will manifest at different times in your life.