The suspension on my 2008 Jeep Wrangler squeaks when I hit a low spot (maybe 4-6" from the grade), even at slow (<10 mph) speeds.
Where can I lubricate or what should i check to eliminate this squeaking?
Claptrap is on the money with grease points, but many modern cars don't have them, and I can't speak to how the Wrangler is setup. That is the perfect starting point, though.
The next step would be to spray down all the rubber mounting points (suspension bushings, shock mounts, etc) with white lithium grease to see if that quiets it down at all. I fear that a normal spray bottle won't be able to get into the 'inside' surfaces of the rubber parts that are causing the squeaks. That leaves you with the final option of unbolting the problem elements so that you can rub some grease on the rubber surfaces. The downside with this solution is that suspension can be very dangerous if you loosen the wrong bolt. In fact, it can be deadly.
So, I would recommend trying the grease points, and the white lithium grease options before proceeding any further. Hopefully, that fixes the issue.