The Duplicate Frame Markers feature is a very cool addition to Premiere and one that I use often. During our logging process we also use clip markers to identify good deliveries. However it doesn't appear that both can be visible on a timeline at the same time. Am I missing something here or is it https://www.adobe.com/cfusion/mmform/index.cfm?name=wishform time?
Clip markers will show in the Source Monitor and on clips in the timeline.
Chances are you need to turn them on first (not at my editing machine right now.)
Look under the wrench in the timeline.
You're not missing anything. You can select one or the other, but not both.