Dynamically creating a drop down list with related data

We are trying to create a training registration form that allows the user to select a specific training from a drop down list. Each training has an associated unique training ID. We would like to capture the ID of the selected training and send it to a custom API we have developed when the survey is completed.
I have seen two examples that show how to populate a drop down using a file/API call, but I don't see how we could include an associated training ID, which is required by our API to complete the training registration.
For example:
1) The survey loads the data for the drop down from a webhook or flat file
2) User selects training they want to register for
3) User completes survey
4) Webhook sends the training ID for the selected training to our API