Firstly, you need to determine (if you don't know already) what the field type i"zWorkspaceSolution" is.
Launch Web Screen Painter, and go into the schema designer.
Go into the "cr" Table, and find "ZWorkspaceSolution" (make sure you have the correct case of each letter).
I'm assuming the "Field Type" should be "SREL" here, note the "SREL Table"
In Schema Designer go to the "SREL Table" noted above and click the table name, there should be a "Foreign Key Field", note what this is. Expand the table's folder, and find the Field noted as the Foreign Key Field, select it and note that "Field Type".
Let's assume that the field is an Integer (which I'd say is the most likely case, but I can't know for certain without looking at your customization), you will want to add this into the text_api file:
INCIDENT.ZWORKSPACESOLUTION=zWorkspaceSolution.INTEGER
(once again, the case is sensitive of the second "zWorkspaceSolution")
Then when you pass the value in the email you want want to specify it as:
%ZWORKSPACESOLUTION=*integer value*
The integer value will NOT be the actual name of the item, for example: "COMUNICACIONES.INSTALACIONES.FALLA DE ENERGÍA ELÉCTRICA", the integer is the numeral id associated to that solution. You will need to obtain the correlating id by reviewing the table where the Workspace Solutions are stored.
NOTE:
It may be possible to introduce additional customization so that you will be able to put the name value, but from previous experience I've seen that spel code was required. If anybody else has any ideas please let us know.