There is a short answer and an obscure answer.
You can't. Events are not accessible internally, so use state variables for logic and emit events to inform external clients about changes.
Access may be possible with assembly. I came across this pattern some time ago, and since events are much cheaper than state storage, it seemed intriguing. It hasn't really caught on, and I'm unsure about risks that might exist with future forks, etc. Certainly not a supported approach, if there is such a thing.
It seems to rely on a client first observing an event externally, and then by passing knowledge of that event into the verify function a contract can confirm such an event does indeed exist. That offers some interesting possibilities, if it works.
It doesn't allow browsing, counting or enumerating events.
Hope it helps.