snapped exhaust stud

Just for the love of god do not snap it (the easy out), then you're in trouble.
The last time I mentioned them the most common advice was this, take your easy-outs and throw them as far away from the issue as possible, that's the best start.

Anyway, personally, I'd be drilling that out (carefully) and then running a tap through it to chase the thread. Tap and die sets aren't expensive or hard to find.
Saved my cylinder head that way.

weld a penny washer onto it and weld a nut onto the penny washer, the heat from the welding will help expand the metals and then you may be able to unscrew the snapped stud, make sure is a good strong weld!

this is what works best for me , shouldnt take a few mins if you can get to someone that has a welder

First thing to do is make a centre mark, it needs to be as central as possible and sort of ball point pen tip sized, without it the drill will wander all over the place.

You also need some form of coolant (WD40 will do) and you need several decent make drills (Or a grinder and the skillz to sharpen them!) you will get through a few.

If it's not stainless then medium pressure and medium/slow speed, as soon as the noise changes then swap drills. If it starts to chatter it'll stop cutting and just chew the drill.

If it's a stainless stud you need to be careful, it doesn't behave like normal steel. You need to push hard and go at a medium speed, as soon as the drill stops biting then stop and swap drills, it must keep cutting all the time. The reason for this is that stainless work hardens like a tw@ and you will quickly end up with an undrillable stud uif you stop cutting and start chattering or rubbing.

If you get to an engineering supplier and buy a centre drill or a spotting drill it'll make starting off much easier, these short stubby drills are super hard and short so they don't flex. The centre drill has a central small drill and a sort of countersink behind, the spotting drill is a very short cobolt steel drill. They are very good at starting holes (It's what they are for) and don't tend to wander as easily.

Once you have a decent central pilot then go for a drill that's a few mm smaller than the hole you need (Not too small it'll just snap) so assuming M8 you want a 6mm drill initially then open it up to 6.8 assuming it's central and you will probably find the remains of the old stud will drop out, if not then drill to 6.8mm and retap it

Failing that open it up to 8mm and use a nut and bolt as above!