Can a rabbi place a Chumash on the Torah to read the book (instead of of reading the Torah, not messianic)

Shalom, Thank you for your question. In general, if there is a Rabbi in synagogue, he is the correct address to ask your question of. However, as you have already written to us – a quick answer is that the holiness of a Torah Scroll is much higher than that of a printed Chumash, and therefore it is forbidden to put anything on top of the Torah Scroll, including a Chumash. A printed Chumash may be placed next to the scroll, and can be looked at for help when reading the scroll. But, it must be stressed that the actual reading must be done from the scroll itself. So, one can look at the printed Chumash to see what the vowels and notes are, and then return one’s gaze to the Torah Scroll to actually read the words written there out loud. Blessings.