Yes you can set most variables with a default value, so for instance if you have 3 variables and the workflow starts these variables will not be empty. 

I think the question rather is, if you can display these default values on the workflow variables overview.

Afaik you cannot. But you can suggest this feature to be included in a future release of nintex: Customer Feedback for Nintex

I think this feature would be useful, good idea! You will receive my vote

Hi Bruce.

Just in case Phillip's answer is not what you are after.

Below is how you set a default value for a workflow variable.

For Nintex Workflow on-prem, you can do this via Workflow Settings->Workflow variables for variables that support default values

(variable such as collection variables do not support default value)

For Nintex Workflow O365, you cannot set a default value for any variables.

Thomas

I believe this was added to user voice here:

https://nintex.uservoice.com/forums/229405-1-nintex-workflow-for-sharepoint/suggestions/11730639-please-list-the-default-values-on-the-workflow-var