To retrieve a list of assessments available in a client's platform, there needs to be a GET call run against the assessment list field.
Example
URL: https://api.icims.com/customers/6269/lists/lists.customfields_lists/node/C18162
Result (truncated):
{
"hidden": false,
"children": [
{
"hidden": false,
"id": "C26217",
"listnodeid": "26217",
"value": "WonscoreBA"
},
{
"hidden": false,
"id": "C26207",
"listnodeid": "26207",
"value": "hiretheright.com - talent management"
},

We were emailed a question asking how to use the list api for background check packages. Here is the api call:
List API Steps for Partner Screening (based on best practices)
ID’s to Know
List ID = lists.customfields_lists
ParentNode (Background Package) = D37002025
ParentNode (Drug Screen Package) = D37002030