Die zweite Version ist besser. Laß das "good" weg, und überlege nochmal, ob Du in so einem Bewerbungsschreiben jeden Satz mit "my" oder "I" anfangen solltest. Im Deutschen ist das sehr schlechter Stil.

"refers" isn't the right word, but I don't know what exactly you want to say there. So, in attempt to pick the right one, what word would you use there in German? Perhaps you mean "is the result of"? Or something like, "I developed my English knowledge during a six month stay in Canada along with my daily work at MTU."?

Beyond that, I like the first one better. Language like, "I feel/I think," to me, sounds rather weak.

My good English knowledge refers to a six-month stay in Canada and my daily work at MTU.
I can quickly adapt to new circumstances. I like to organise and work in teams with other
people.

OR

My good English knowledge refers to a six-month stay in Canada and my daily work at MTU, I feel that I would be able to quickly adapt to new circumstances. I like to organise and work in teams with other
people.

I would write something like this instead:
"My excellent grasp of the English language stems from a six-month stay in Canada and my daily work at MTU. I feel that I can quickly adapt to new circumstances; I am also able to organize and work well as part of a team."

Saying "in teams with other people" is redundant, because "team" already assumes that.

Wait...does MTU refer to Michigan Technological University, by any chance?

Ich will ausdrpcken, dass ich gut Englisch Sprechen kann, weil ich sechs Monate in Kanada war und bei meiner Werkstudentenstelle auch viel Englisch rede.

Ich bin auch nicht wirklich zufrieden mit der Formulierung, aber mir fällt auch nichts besseres ein.
Habt ihr noch weitere Vorschläge?

MTU = Motoren und Triebwerk Union! :-)

Benopposite's seems pretty good.

no problem...but perhaps you could help me?
related discussion: bigger guys with bigger trumpets - Der neuest...

I could distinctly improve my spoken and written english during a six month stay...

nur ein vorschlag

No, sorry, the previous suggestions were better.

I could = Ich könnte
I was able to = Ich konnte