You can allow students to like replies in a discussion. If a discussion allows liking, users will see a Like icon within each discussion reply. By default, liking is available to all users in the course; however, you can choose to restrict the option to graders only.
The Like icon is enabled on a per-discussion basis.
Learn how to like a discussion reply.
In Course Navigation, click the Discussions link.
Click the Add Discussion button.
Create your discussion. Enter a discussion title in the Topic Title field . Add discussion content using the Rich Content Editor . Select sections for the discussion in the Post to drop-down menu .
Set Liking Options
In discussion options, click the Allow liking checkbox .
When you allow discussion likes, you can select two additional options.
Only graders can like : select this checkbox if you want to limit the liking functionality to only graders in the course, which means only users with the Edit Grades permission can see the Like link. However, all users still see the total number of likes for each reply.
Sort by likes : select this checkbox if you want the discussion to sort replies by the number of likes. Sorting cannot be changed by any users unless you remove the sorting setting. This option may take at least 10 seconds to cache the page and view sorting appropriately.
Discussion replies are sorted in descending order. In threaded discussions, replies retain the associated parent. For example, a new discussion may receive two replies. Then, Reply 1 gets individual replies a, b, and c, and Reply 2 gets individual reply d. If Reply 2 itself is liked, and reply b is liked, the discussion threads will be sorted first with Reply 2 (and reply d), then Reply 1 with reordered replies of b, a, and c.
Save and Publish
If you are ready to publish your discussion, click the Save & Publish button . If you want to create a draft of your discussion and publish it later, click the Save button .
Publish Saved Discussion
When your discussion is saved in a draft state, you can return to the page and publish it at any time by clicking the Publish button in the classic Discussions interface  or the Publish icon in the Discussions Redesign interface .