You need to subscribe the Reference Data Providers Service first

Problem: 

When I click the Browser button on the Reference Data tab for Configuring Composite Domain to Use Reference Data Service, nothing shows up in the Online Reference Data Services dialog box.

Reason: 

I have not subscribed any Online Data Providers Services

Solution: 

Go to https://datamarket.azure.com/browse/Data?Category=dqs, subscribe the service you need. Free for a low volume validation.