Do you have a copy of your Action Type UID that the workflow is associated with? If so, you can use it as a parameter within the GET /api/v2/actions endpoint to return a list of the values submitted, such as criticality. If you don't the Action Type UID already, you can retrieve it by running the GET /api/v2/actions/types endpoint first and filter for the Action Type's name associated with the workflow in question (see screenshot below). The UID shown below the name is the UID of the Action, which could also be searched in an empty GET /api/v2/actions endpoint call to get its associated Action Type UID.
The key to getting the extra details / values returned from the GET /api/v2/actions endpoint is to specify the actionTypeUid parameter. Without it, the details aren't returned. However, if the API call is made for a specific Action Type, then the values will be returned. Here's an example from the API UI in my internal instance:
And the response with some fields trimmed to keep it cleaner to paste:
{
"pageSize": 5,
"pageNum": 1,
"total": 14,
"items": [
{
"Uid": "5cc80c3d-1466-463a-b482-40db3e76c9cd",
"ActionTypeUid": "331d2417-150f-41b6-9228-df6c884d317f",
"ActionTypeName": "API Test",
"CreatedOn": "2021-12-29T20:48:29.903Z",
"ProblemDesc": "<p>test for api field lookups</p>",
"Criticality": "Critical",
...
},
...