Short answer: The word "abklopfen" in this context can be translated to something like "check for".
The physical process of "abklopfen" is widely used in everyday life. A doctor might tap at certain areas of your body to find out if you are ill, a security guard might pat you down to check for hidden weapons, when buying fresh fruits you might tap on them to check if they are still good, you might tap on a wall/construction to hear how it sounds and to find out about its quality, etc.
This lead to the word "abklopfen" to also be used in a figurative sense when saying that you extensively check something. In this sense, it is a little similar to the proverb
Etwas auf Herz und Nieren prüfen.
which (according to my dictionary, I haven't heard the English form myself) can be translated as
To put something to the acid test.
Your sentence could thus be translated into English as
While at it, she looked at dream jobs that are doable and checked them for a gap between wish and reality.
edit: Regarding the question if it would be better to use "zwischen" here instead of "von" I would say no, the "von" is the right expression to use.
To be clear: You can use both, but "von" is, in my eyes, the better choice. Let's look at the two different terms, together with their noun "Diskrepanz" to illustrate the difference:
- "Zwischen" means "between", so saying "...die Diskrepanz zwischen A und B..." means that we compare A and B and find a discrepancy there. For example:
Die Diskrepanz zwischen den prognostizierten Kosten und den tatsächlichen Kosten betrug 100 Millionen.
- "Von" means "of", so saying "...die Diskrepanz von A und B" would mean that A and B together form a set that has in itself a discrepancy.
Thus, you would use "zwischen" if you have two distinguished objects you are looking at, and "von" if your two objects form a strongly related set (e.g. Wunsch/Wirklichkeit, Realität/Fiktion, Tag/Nacht,...). The lines are rather blurry here and you can use either "zwischen" or "von" without anyone blaming you.
To finish, let's look at cases of "Diskrepanz" where the use is clearer:
Die Diskrepanz von 20% in der Berechnung...
Here, we have a discrepancy of 20% in our calculations and the only appropriate term is "von".
Die Diskrepanz in den Ergebnissen der Studie...
Here, we have a discrepancy (in the sense of "contradiction") in the results of a study, thus the only word that fits this case is "in".