Cannon find the pause button in this version?

Switch of "Simplified Easy mode"
http://www.microsystools.com/products/sitemap-generator/help/easy-sitemap-generator-mode/

This will make all options visible. ~99% of all options are otherwise hidden to avoid scaring off new users


Doing that, you will have "Start scan", "Stop scan" and then some checkboxes (instead of "push buttons", but otherwise they work exactly the same way) where you can select if "Start scan" should resume an earlier scan.
http://www.microsystools.com/products/sitemap-generator/help/sitemap-generator-resume-scan/

(Yes, the help should be updated to use "check boxes" instead of "push buttons", but the two things behave exactly the same way.)