1. Preheat a grill to medium-high. Toss the shrimp with 2 tablespoons adobo, 2 tablespoons vegetable oil and salt. Let stand while you toast the pepitas and make the dressing.
2. Heat a large dry skillet over medium heat. Add the pepitas and toast, stirring occasionally, until browned in spots, about 8 minutes. Set aside.
3. Puree 1 cup cotija, 1 cup cilantro, the juice of 2 limes, the juice of 1 orange, avocado, the remaining 1 tablespoon adobo and the remaining 1/2 cup oil until smooth. Transfer to a medium bowl with the jicama.
4. Toss the cabbage with the juice of the remaining orange and the remaining lime in another medium bowl. Season with salt.
5. Grill the corn, turning occasionally, until tender and charred in spots, about 15 minutes. Cut the kernels from the cob and add them to the bowl with the jicama and dressing. Toss to coat.
6. Grill the shrimp, turning once, until charred on both sides and just cooked through, 2 1/2 to 3 minutes per side.
7. Divide the cabbage among 4 plates, and then top with the jicama and corn mixture, followed by the shrimp. Sprinkle with the pepitas and the remaining 1/4 cup each cilantro and cotija. Serve with lime wedges.