For setting Item Key, go to System Tab ->Workflow ->Work Queues and choose the Work Queue for which you want to set the item key on the right pane. Under Queue Details, you can find an input field 'Key Name'. Give the name of the field/column name; this will be considered as 'Item Key' and will be populated on loading data in to work queue.
I am also facing same issue, I am trying to put the file names in place of item key in work queue. while adding the data into queue i am using single row collection. i have defined the column/field name like "SinglerowCollection.Filename" in the "System Tab ->Workflow ->Work Queues " section. but i am not getting the defined file names in "item key" field.
1. I pulled in my raw data from an excel file
2. I then added a collection and an action to add a row to the collection.
3. Loop through the raw data and use a multicalc to combine the fields from the original collection into one field. I named mine "Key". Then the loop will store it into the new collection.
4. Once it's done looping through the original collection, add the updated collection to the queue and call your key field "Key" and it will the fields combined.