Your code iterating through the items in st2 (collection of objects) and extract the UserJobTitle property from each item. If you only need the last UserJobTitle in the loop and want to use it in another place (like a TextBox), then refer to the Solution-2.
If you want to set the value in another place (like a TextBox) upon a condition then you can modify your code as:
if (st2 != null)
{
foreach (var item in st2)
{
if(Convert.ToString(item.UserJobTitle) == "AnyJobTitle")
{
textBoxJobTitle.Text = Convert.ToString(item.UserJobTitle);
}
}
}