because of his quick learning skills, X was able to familiarize himself with (his) new responsibilities/tasks in no time

e.g.

... I vote for 'perception': Siehe Wörterbuch: perception . . .

language is rarely a democracy, Daddy. :-)

... let's see what Carly makes of it . . . ;-)

Was mit 'quick' finde ich auch gut - quick mind?

I see Auffassungsgabe as the "talent" or "skill" with which one is able to comprehend something

LEO sagt so: Siehe Wörterbuch: Auffassungsgabe . . .

Had a bit of trouble with my Internet connection, though NO Northern lights in sight :-((

dude, I don't want to post too much of X's background, but s/he's not new to the business. Should have mentioned, that this is in a letter of reference.

I don't quite agree with LEO on most of its suggestions there. :-)

@Carly: I dont think I gave away too much, did I? Especially since I have no idea who this is about.

how about "quick grasp of new concepts"?

Eine zwar nicht ganz deckungsgleiche aber ähnlich "abgedroschene" Floskel, die zumindest in eine ähnliche Richtung geht ist "able to think on their feet".

You gave away nothing, dude :-) I didn't give away enough.

What about this combination: quick mind and keen perception?? His/Her talents and skills are specifically mentioned in other parts of the letter.

edit: Hadn't seen Marianne and Lady Grey drop by until I hit Absenden. X periodically takes on new responsibilities/ functions, in addition to the ones s/he already has.

Being extraordinary quick on the uptake, he ...

extraordinarily - schalt' doch mal Deine PM-Funktion ein, damit man diskret verbessern kann, Reinhard.

Reinhard, ja - aber das paßt nicht wirklich in ein Zeugnis, finde ich zumindest.

Lady Grey: Danke für die Korrektur. Ich bin zwar kein Tierarzt, aber ich dachte doch gerade an den Grundsatz: "It Shouldn't Happen to a Vet!"
(Du kennst wahrscheinlich die "alte" Serie und weißt warum.)
Ist mir peinlich. :-(

In our report cards it used to say comprehension for Auffassungsgabe

I find 'quick on the uptake' (#13) not bad.

Today I translated the phrase on the hoof as 'is very quick to assess situations'.

I like Marianne's "quick grasp"

Because of his/her quick grasp (of new concepts/tasks/etc), s/he takes little time to be comfortable with new functions.

Today I translated the phrase on the hoof as 'is very quick to assess situations'.

War der zu übersetzende Satz "on the hoof"? Oder hast Du gedolmetscht? Or were you just thinking on your feet? ;-)
Meine sonst passable Auffassungsgabe lässt mich gerade im Stich.

Suggestion:
X is a fast learner whom we have learned we can rely on, regardless of the difficulty of the task to hand or the novelty of the challenge.

Because of his quick intellectual grasp ...

(falls das nicht doppelt gemoppelt ist)

... and you will be lucky to get him/her working for you . . .

... ambiguity intended . . . ;-))

OT@Reinhard - What a coincidence - I'm currently reading Alf Wight's (James Herriot) biography, written by his son. Wonderful book!

I sent off various suggestions to customer, and X settled on "Because of his quick mind and keen perception, X rapidly familiarized himself with new responsibilities..." - X works at the upper management level, and the sentence goes on for about another two lines :-)

Thanks, everybody!