I would prefer the second option,
participated in the online webinar ‘Engineering Projects Management’
The first example isn't wrong, but it needs at least a comma after webinar. Better yet would be the word named instead of a comma,
participated in an online webinar named ‘Engineering Projects Management’
In the second option, the name of the course is in apposition to "the online webinar". That fits because they are both specific expressions.
I don't think "an online webinar" makes a good appositive for the exact
course name, so the descriptive phrase "named..." fits better.
On the other hand, if the order of the phrases is changed,
participated in ‘Engineering Projects Management’, an online webinar
then an fits, because you've used the more specific phrase first, and added a descriptive phrase after it.