Hi Jasper,
I also think that curiosity is more a personal trait that a skill. But sometimes it can be trained when you think about it together with learning and communication. From my point of view, a tester should be curios to discover defects, to ask as many questions as possible in order to find out any detail about the product and he/she must be always critical and focused on details. But the tester must be also very capable to learn and understand the product and its behavior. This is done by a continuous learning and a good communication within his/her team and I think these skills can be trained. Maybe some of the testers do not have very good communication skills or do not learn very fast or are not very curios while testing. But the combination of all these 3 things can be trained and with more and more practice it can be improved. Each different situation while working as a tester can be a good exercise for a tester to help improve any of these things.
That’s why I see curiosity a personal trait but also something that a tester must combine with other skills to become a good tester and do his/her job in a very good way.
Regards,
Alin