Ah, the simple client… A very good example of how not to make an OPC-UA client. 
The namespace you are looking for is:
uri://ip.ip.ip.ip/Ignition%20OPC-UA%20Server
When using the UA-Expert client, you will see this is entry #1 in the namespace array (aka NS1). In any other client i know, you use the index instead of the value…