Hello @unclespeedo -- welcome back!
To answer the question asked, I think you would need to format the sku_list.value as an Object and then call upon the sku property to have it use the array. You will, however, most likely need to take this array and use your DB's string_split method to actually format the array properly for the query.
This:
select customerName from retooldb where sku in ({{sku_list.value.sku}})
would look more like
select customerName from retooldb where sku in (SELECT * FROM string_split( {{formatDataAsObject(sku_list.value).sku.toString() }}, ',') )
as noted here you will need to use the Postgresql version with unnest