Learning reinforcements are really any feature that’s going to enhance the learning experience for your students. Basic learning reinforcement features are progress tracking, quizzes and assignments, video bookmarking, and certificates, just to name a few.
Both LifterLMS and Kajabi offer learning reinforcements, but LifterLMS has an advantage over Kajabi because of its ability to customize and advanced quizzing features. Note that these features are paid add-ons with LifterLMS, or on the Infinity Plan, so if they’re appealing to you, budget accordingly. 
LifterLMS offers graded quizzes, and a variety of question types from multiple-choice, true or false, picture choices, fill-in-the-blank, long and short answers, and more. Any type of quiz you can imagine can be built on LifterLMS. They offer reports on quiz results as well, be it individual per user, or a group of students. You can use these reports to see how your students are absorbing the materials.
They offer assignments, which can be a task or task list, upload requirement, or a long answer requirement. LifterLMS has certificates as well, where you can add details and merge fields. It comes with a provided background, or you can upload your own.
They don’t have advanced progress tracking built into their plugin, but you can find add-ons that provide basic progress tracking.
Kajabi does offer a few learning reinforcements to enhance the learning experience.
The assignment features allow the functionality to add different question types, like multiple choice or long-answer. These results can be viewed from your People tab under each user.
The assignments feature takes the place of any quiz or test functionality on Kajabi.
Progress tracking can be viewed from the backend, but there’s no way to display the progress to your students.
Kajabi does support videos and audio, but there’s no bookmarking.
For example, with AccessAlly, you can set a progress objective to be 5 minutes for example into a video. The user will have to watch that video 5 minutes before their objective would be complete, or you could set it up that it has to be complete before they can move on.
Nothing like that can be achieved with LifterLMS or Kajabi.