You can learn more how Knapsack Pro API works:
Regular Mode - deterministic tests split across parallel CI nodes.
Docs: How knapsack_pro gem works in Regular Mode.
Queue Mode - dynamic tests split across parallel CI nodes.
Docs: How knapsack_pro gem works in Queue Mode.
Here you can find API documentation for Regular Mode and Queue Mode. The API documentation might be useful if you want to build client tool to directly integrate with Knapsack Pro API.
You may also find useful article with examples how to extract timing data for recorded CI builds using API.