If the massive blackhole at the center of our galaxy suddenly beltd out a Quasar,would we see it as a beam ?

If enough gas or a (disrupted) star fall into the 4 million solar mass black hole at the center of our galaxy it will indeed become "active" again. Whether "only" as an active galaxy nuclei or (also) als a quasar depends on luminosity and viewing angle. There most probably will be a jet again. Whether we can see it depends ond the unknown rotational axis angle of the black hole. we can't tell yet. But the jet will illuminate the surrounding gas, and this will be very probably seen as x-rays.

Note that the galactic center was more active even 100-300 years ago as can be seen in form of glowing gas clouds in its neighbourhood. It is very likely that _sometime_ the black hole gets more active again.

First off Quasars almost certainly do not exist in our universe anymore. Yes, we see them out there but they are extremely distant and thus we are looking back to the very young universe. There are none at closer distances so we can surmise they no longer exist.

If you mean would we see the jets of matter if the black hole in the center of our galaxy started "feeding" again then yes and no. Yes if you have a telescope but you would probably not see it by just looking. The center of our galaxy is very far away from us.

It probably would not affect us at all. Even if it was pointed at us at this distance the effect would be minimal. That said the jets would almost certainly be pointed out the "top" and "bottom" of the galaxy thus nowhere near us. In short we'd be fine.

The beam would have to be in the visible spectrum, which it is not. The beam may strick material which could fluoresce into visible wavelengths, but that's hypothetical.

While I am not sure of the mass of the black hole at the Milky Way's center, I am fairly certain it's not anywhere near the mass necessary to erupt into a quasar.