The simpler question "Is that possible?" would be "그것이 가능합니까?", or "그게 가능해요?" more informally. Adding the sense of "even" can be done in a couple of ways. 1. 그게 가능하기는 합니까/해요? 2. 그게 가능하기나 합니까/해요? (1) sounds like a simple question of wanting to know, while (2) has the connotation of strongly doubting it (i.e. it can sound rhetorical). This is because 나 in 가능하기나 functions like 은/는 (among other meanings) but has a strong emphasis.