Can I get some help/example on how to get the file translation progress percentage from Forge by using web-hook API in C#?
You can find many samples on https://github.com/Autodesk-Forge. For C# examples around webhook, try https://github.com/Autodesk-Forge?q=webhook&type=&language=c%23.
In order to track the progress of your file translation, you can simply create a webhook for the extraction.updated event, and then use the Modle Derivative endpoint GET /modelderivative/v2/designdata/:urn/manifest to retrieve the JSON manifest which will include the status of the translation for the entire document as well as the translation status of its individual 2D or 3D outputs.