I am afraid there is not a general access to get do the getting similar to wks.labels command in LabTalk. For user parameter rows, you can use wks.userparam1 etc to control, see this new blog post:
http://blog.originlab.com/2015/show-columns-mean-and-size-in-column-label-rows#more-727
The following OriginC code will provide this function, and you can add this to your OriginC codes and put into Code Builder User (AutoLoad)
//usage: v1 = IsWksLabelShown("C");
// return 1 if Shown, 0 if not, <0 if error
int IsWksLabelShown(string strLabelChar)
{
Worksheet wks = Project.ActiveLayer();
if ( !wks )
return -1;
vector<int> vnTypes;
if ( !okutil_convert_labels_string_to_indices(strLabelChar, &vnTypes) )
return -2;
// must input only one label type
if(vnTypes.GetSize() != 1)
return -3;
return wks.IsLabelTypeShown(vnTypes[0]) ? 1:0;
}