OPC Labs runs a public OPC UA sample server that you can use for your explorations and tests. The server is located on opcua.demo-this.com, and its endpoint URLs are:
Our example code also refers to this server, so that the examples can be run without having to set up a server locally.
The server is based on the sample server code from OPC Foundation.
For OPC UA Alarms&Conditions, see Public QuickStart Alarm Condition Server (OPC UA).