The lower-case() function is an XPath v2 feature, so it appears DevTest is using an v1.x version.
So, with some googling it appears that a translate function could do the trick. It makes the Xpath much longer so you'll have to edit it in a text editor and copy-paste into DevTest assertion pane.
//*[translate(text(),'ABCDEFGHIJKLMNOPQRSTUVWXYZ','abcdefghijklmnopqrstuvwxyz')='training']
The above one obviously only for 'training', if that one works you can expand it with the | (OR) constructs
//*[translate(text(),'ABCDEFGHIJKLMNOPQRSTUVWXYZ','abcdefghijklmnopqrstuvwxyz')='training' | translate(text(),'ABCDEFGHIJKLMNOPQRSTUVWXYZ','abcdefghijklmnopqrstuvwxyz')='education' | translate(text(),'ABCDEFGHIJKLMNOPQRSTUVWXYZ','abcdefghijklmnopqrstuvwxyz')='solutions']
Hope this helps,
Danny