What do I feed my mali uromastyx? and how is he even alive after this?

three months without proper care plus how much proper care did he get before? he probably has metabolic bone disease. Uros need very high heat and a specific diet of healthy greens and calcium supplement, plus UVB. A healthy uro does not need water they get it from their greens. Take him to a reptile vet, or maybe find a reptile rescue who will take him on.