Within the variable menu you should be able to see where a variable is being used (what actions) within the workflow.
If you need to find and replace a variable within the workflow designer (such as needing to change a variable's type), when working with large workflows it is hard to find where the variables are being used, but you cannot update/remove the variable until all instances are removed from existing actions.
Thank you for your suggestion. This feature was released back in November 2022, allowing designers to see where variables are being used, and also navigate to the usage within the workflow design. For more information, please see this help document: https://help.nintex.com/en-US/nwc/Content/Designer/UseVariablesinWorkflow.htm#View