Unfortunately, the ability to preview the contents of an imported query/selection directly isn’t currently a feature of CRM. Imported selections don’t work exactly like Ad-Hoc query-generated selections (which can be previewed with View Selections). The only way you can browse the records of an imported selection is to use ad-hoc query to query on the Imported Selection, with no real criteria, and then click Preview Results. Remember to use the import option to Show the selection in Query, in order for it to be available.

It would be helpful to be able to preview them just like ad-hoc selections.