Unless switched, romex type residential wiring generally contains 3 conductors. 2 current carrying and 1 ground. The circuit starts at the house panel, then daisy-chains to each successive outlet in the circuit, so each outlet is wired in parallel. The US uses a start/stop approach, the UK uses a circular approach. At least one of those wires will be landed to a breaker, if a 115v system, both will be landed to a double breaker if a 230v system.
This also means that in every outlet box, there's a ground coming from panel to previous outlet and a ground going to the next outlet in continuity.
It's quite hard to just 'add' a ground to any one particular outlet. It's far easier to trace the wire path, find where the 'break' in the continuous ground is, and fix it. This can be done by the homeowner, but can often require someone with electrical knowledge and understanding to find and fix. As said prior, the only time you'll not/rarely find a ground is in a very old building, as they served no purpose at that time, being a simple 2 prong, not the modern 3 prong outlets.
To fix that kind of wiring problem and bring the wiring upto current code requirements would entail a complete reworking of the entire electrical system in the house. So hopefully, your wiring is new enough where backtracking the circuit would reveal where exactly you dropped the ground.