How to lubricate noisy joint on Dahon foldable bike?
For similar things on cars I use white lithium grease (e.g. this stuff on Amazon)—it is a good lubricant and sticks around the joint that you apply it to.

Any similar thick grease should work for this joint, but the crucial thing is getting it into the right place.  Taking the joint apart and applying grease to the mating surfaces is the best bet.