In DQ+, the Uniqueness Check node is DQ+'s native way of checking for duplicate values between records in an analysis. To use it, click on the "Data Quality" option on the pane to the left, then in the list of nodes that appear, drag a "Uniqueness Check" node into your analysis.
When you click on the node, you'll see a window to add a field. You can add either an exact match comparison or an expression.
When you run/test the analysis, it will show a true or false if there is an exact match of a field's values between two records. True if it's unique, false if it's not.