If you go to the header area in the note panel you can customize the toolbar there to include the reminder icon. Right click on the info icon, select customize toolbar, and then drag the reminder icon to that toolbar. Looks like this afterwards.
Two things that may pertain:
In the Windows client, reminders are only shown in Snippet View, Card View, and Thumbnail. THey are not shown in either the Top List or Side List views.
In addition, in the views that they can be shown, reminders are only shown for your current context; if you have navigated to a notebook that contains no notes with reminders, then they are not shown. If you do a search, and the search results contains notes that have reminders, then those reminders are shown.