What is the best way for tagging someone witout other co-workers

If I understand your question, to tag a coworker when posting in a Workplace workgroup, you can either select "Add to your post", click on "Tag coworkers" and then start typing their name OR within your post, type @ and then start typing their name. Either way, coworkersnames will start to appear and you select the one you want. After you publish your post using either method, the tagged coworker will receive a notification that they were tagged in a post by you.