There is no subject. "Indicating" is a present participle acting as a modifier.
Student or Learner
Each pile is driven to refusal, the point at which little additional penetration is made with continuing blows of the hammer, indicating that the pile is firmly embedded in the bearing layer.
What is the subject of indicating in red?
Then, can you tell me what is indicating that phrase? Is it just a word or the whole sentence in front?