How do I connect a C-wire on a Triangle Tube Prestige Solo 110?
The 24V transformer is part of the control board, and so is not shown on the wiring diagram you've linked to. However, R is always one side of the transformers secondary, and C is always the other side. The thermostat needs to draw its own power, and so requires a connection to "C" to complete the circuit.



Your thermostat is just a load on the 24V circuit.



If you don't feel comfortable modifying the wiring, it's probably best to contact a local HVAC technician.