There is debate about whether おなじ気 is referring to the amount of Ki or the general feeling of Ki. I looked up the Japanese text and wondered if the lack of a の character might shed any light.
同じの気 wouldn't be grammatical. 同じ fixes alone to a noun. And maybe you could say something like なにかする気の(が) 同じ人 but this sounds really unnecessary.
Judging from just that panel my interpretation is Gohan is sensing the feel of Goku's Ki. Especially if Goku isn't present in that scene.