You can check it after obtaining current style of page element: font-style for italic, font-weight for bold and text-decoration for underline.
In Internet Explorer every page element has currentStyle property. In other browsers (as well as IE 9+) page object has contentDocument.defaultView.getComputedStyle function to get current style for a web page element.
function getCurrentStyle(page, webobj, propName)
{
var style = page.contentDocument.defaultView.getComputedStyle(webobj, "");
return style.getPropertyValue(propName);
}
function test()
{
var page = Sys.Browser("*").Page("*");
Log.Message(getCurrentStyle(page, page.Child(0), "font-style"));
}