Howdy,
Here are a couple of quick ways:
1. Type in the Search box (upper right): Mozart
2. If (1) provides too many undesired items, type in the Search box a query. Example: [Composer]=Mozart
3. If you are going to routinely want to view by Composers, create or modify a view that includes Composer as a category or pane. For example, modify a copy of the Artists view. Right-click the Artists view in the tree (on the left) under Audio and select Customize View. Remove the Album Artist (auto) entry, and then click Add and select Composer. Move Composer to the top of the categories list. Click OK and save a copy of the view naming it Composers.