As far as I know there is no way of uncovering the Google 'not provided' keywords, and I don't think there's any point in kicking against it either because there are several ways that you can get information. Mostly I think Google tries to hide any terms it thinks may release confidential information or very specific low-volume terms, in which case these probably wouldn't be much use anyway.
With enough traffic you can still get an awful lot of information from Google Analytics, it still releases about 10% of the keywords.
Secondly, Look at Google Search Console > Search Traffic > Search Analytics.
The strategy that I like best is to work the opposite way on, decide on the keywords that you want to go after and then optimise the site for those keywords.