What is the difference between sharing knowledge and sharing an idea?

You can use the Share Knowledge post type when you want to bring attention to a post under that category. Users earn +5 points every time they make a knowledge post. Subsequently, they earn an additional +1 point for each like and comment on their post.

You can use the Share Idea post type when you have a plan/idea that you want others to participate in (possibly) and you would like to see that implemented in some way. Users earn +10 points every time they make a Share Idea post. Subsequently, they earn an additional +10 points for each comment on their post.

Note: Users can earn points only if the Rewards & Gamification is enabled for their organization.