UIFont does not have a bold/italic/... property, so you will have to rely on the font name only. This will be a problem if you don't know which fonts will be used.
In the case you know that you will use eg. only Helvetica you can try this:
UIFont *font = textview.font;
if([font.fontName isEqualToString:@"Helvetica-Bold"])
NSLog(@"It's Bold!");
Alternatively you can search font.fontName for the word "bold"/"medium"/"light" etc., but that's not a guarantee you will get something from every available font:
if ([font.fontName rangeOfString:@"bold" options:NSCaseInsensitiveSearch].location == NSNotFound) {
NSLog(@"font is not bold");
} else {
NSLog(@"font is bold!");
}
// if font.fontName contains "medium"....
// if font.fontName contains "italic"....
Check http://iosfonts.com/ for the available font names.