Two pads with holes about 1mm diameter, about 1/2 inch apart, both grounded.
Solder a thick wire rail to these, like a hitching post outside a Western saloon, and you'll have a secure place for the crocodile clips on your scope ground leads.
If you're going on to a small production run, (50 or so) consider identifying every net that doesn't naturally connect to an external connector, and connecting it to a pin on a ribbon cable header (or a few small 10-way headers). This can be a lower budget option than adding test points for a "bed of nails" fixture.
Then you can build a test fixture that attaches to your board with just a few ribbon cables, and allows you to test for things like shorts to power or ground without the expense of a full "bed of nails" fixture.
See Majenko's answer to this Q&A for a really neat trick with staggered pins, to make good connection without fitting sockets...