Extract characters

That works for OCWN111111111, but it does not work for DENWN11111111 or DTWWN11111111.

Strange. Seems to not like using Part or Left. You can probably look at something like:
var text t = "DTWWN11111111";
If(
    Right(Left($t,6),2)="WN",Left($t,4),
    Right(Left($t,5),2)="WN",Left($t,3),
    Right(Left($t,4),2)="WN",Left($t,2),
    Right(Left($t,3),2)="WN",Left($t,1),
"")

Basically look at the first 6 characters - if the last two are WN - get everything to the left, if its not WN - look at the first 5, trying to find a WN. 

Chayce Duncan | Technical Lead
(720) 739-1406 | chayceduncan@quandarycg.com
Quandary Knowledge Base

It gives me an error message to check the sytax.

var text t=[Incident Number];
If(
    Right(Left($[Incident Number],6),2)="WN",Left($[Incident Number],4),
    Right(Left($[Incident Number],5),2)="WN",Left($[Incident Number],3),
    Right(Left($[Incident Number],4),2)="WN",Left($[Incident Number],2),
    Right(Left($[Incident Number],3),2)="WN",Left($[Incident Number],1),
"")

How can you make it work with lower case "wn"?

Try this

var text ReplaceWNwithPipe = SearchAndReplace(Upper([data field]),"WN","|");

Left($ReplaceWNwithPipe,"|")

Thank you!  This worked!  I appreciate the help!