Collocations for challenging - adj.

be, prove
make sth
We have changed the course to make it more challenging.

find sth
He found the course academically challenging.

extremely, fairly, very, etc.
enough, sufficiently
The tasks were not challenging enough for me and I got bored.

academically, intellectually, physically, politically, technically

Challenging is used with these nouns:
job, look, question, target, task, work