What is the meaning of "Your eyes should be open"?
Radak: Your guarding should be constant in this place.
Why does it say "El ha'Makom ha'Zeh"?
Radak: This is like ba'Makom ha'Zeh. Also "v'El ha'Aron Titen Es ha'Edus" (Shemos 25:21) is like uva'Aron. There are others cases like this in this Parshah - El ha'Makom, El ha'Bayis. Also Yonason translates in 1 this place.
Our text of Yonason says ?l. (PF)
Is Hashem's name being there the same as His eyes being open?
Malbim: No. When Yisrael merit, the primary Shechinah is below, between the staves of the Aron. Then Hashem's eyes are open in the Bayis itself. When Yisrael do not merit, only His name dwells below; the primary Shechinah is above. However, the prayers in this Bayis will ascend on a ladder and Hashem will accept them.