For binding to something of a datacontext, it needs to be exposed via public getter / setter...
public class mainmenusql
{
public List<string> _Jobs
{ get ; protected set; }
public mainmenusql()
{
_Jobs = new List<string>();
// rest of populating your data
}
}
The binding in your window control is the ItemsSource
<ComboBox ItemsSource="{Binding Path=_Jobs}" />
The "DataContext" is applied to the entire window... From that being the basis, any of your controls can have their element "bound" to almost anything "publicly" available ON your data context... in this case, a ComboBox list of choices comes from its "ItemSource" property... So you want the ITEMSOURCE pointing to your _Jobs.