If you are dealing with any unconscious patient the priority is ABC and urgent removal to hospital.

Recognition of  a internal bleed is  patient is pale, cold, clammy-becoming blue-gray if the bleeding continues. Rapid weak pulse (radial pulse will fade with low blood pressure) rapid shallow bleeding etc etc. Signs of shock

Mechanism of injury plays a large part and any abdominal injury in a pregnant lady needs medical attention, but don’t forget that it might be a spontaneous bleed with no outside trauma.

Detecting a internal bleed is a very hard job and unless it is a severe bleed it unlikely that a first aider  or pre hospital care provider will diagnose this.

I guess if the patient is loosing blood from orifices then that will give a large clue to most first aiders.

I think your students  will be very unlucky if they ever come across that type of injury.