(You have to buy LearnDash Plugin HERE)
After Install and active LearnDash Plugin Install LearnDash Demo
LearnDash Login Register
When Learndash LMS Plugin active and user are not login then pop will works
Also enable registration from Learndash > Settings > General.
Head over to Settings » General page in your WordPress admin area. Scroll down to the ‘Membership’ section and check the box next to ‘Anyone can register’ option.
For more customization options, visit the official documentation site of LearnDash from HERE