Hi there thanks for posting in the community! You can easily see what other already-existing tags are applied to other shapes in your canvas. To do so select the new shape you want to tag click on the Tag icon from the Context Toolbar and view the list of tags in the pop-out menu. Any tag with a white background and colored border is applied to a different shape in the canvas but not the current selection. 

If in this example I wanted to re-use and apply the tag “high priority” I simply need to click on the tag in the menu to add it to the selected shape. 

For more information please view this Tagging article from our Help Center and post any additional questions below.