How to protect my rosewood?  

Why would there be any...
Why would there be any problem with placing glass on the furniture?
Go to your local glass shop and ask them what they recommend.
They'll know exactly what you need in terms of type of glass and thickness. It's going to be custom cut and will be expensive.

I'll take good care of it...
I'll take good care of it for you.
It would be my pleasure.

My only piece of advice would be to keep the unit out of direct sunlight.
It may sound obvious but I was caught out once with a lovely rosewood piece that had just been repolished. I put it into a bright spot in the room with a lamp sat on top. Eight weeks later I moved the lamp to find a 'shadow' of the lamps footprint left behind.
This is much more of a problem with freshly polished timber but you have been warned, I'd hate to see that lovely grain pattern messed with.

Thanks
H.moon, Thanks for the advice, I currently have it in a spot that does not receive any direct sunlight and there are no air vents near by. So would you leave the top uncovered?

You can put glass over the top if you want the assurance of a protective barrier.
It depends what sort of wear you anticipate the sideboard will get.
I should imagine something as beautiful as that will just have a few ornaments placed on top that rarely get moved.
If you think it may be exposed to some more physical forms of abrasion like keys and coins scraped across the surface then go for the glass.
Personally I don't like to see glass sat on top of furniture.

I have three just like that...
I have three just like that , two have glass, one does not and yes the one with out glass has faded, I have glass on my desk, and lamp table.

The glass top would simply look tacky.
unless you also have matching plastic covers on all lamps and upholstered pieces within viewing sight. It's called PATINA!! Embrace it.
Just my opinion FWIW.

Another vote
For no glass.

ps
what a beautiful credenza!
All my best,
Mark

It'd be a shame to put glass on it, I think
Wood's not THAT fragile, so long as civilized adults are living in the house.
If you avoid putting rough terracotta pottery, wet umbrellas, or iced drinks atop it, it'll be fine.
If you have genuine concern about the pieces you intend to display harming it, put removable felt on the bottoms of those items.

Thanks
Thanks to everyone for the input. We are a mellow household. No glass it is.

rorschach test?
That is one stunning rosewood work. What type of rosewood is it? The no glass decision is a good one - as stated it would seem tacky and ultimately will not save your rosewood from its natural #1 enemy - light. Attached is a pic of the rosewood from my circa 1940 credenza. Top is the interior of one of the doors and the bottom pic is of the exterior and shows the extreme fading from years of exposure to a large picture window by the original owners who were oblivious to the beauty or value of the piece as evidenced by the fact that I bought it for less than the cost of a great bottle of Amarone, which I bought later the same day to celebrate the find.
Congrats! C'est fantastique!

.
If you ever do and it sounds like you've been convinced not to but...I reckon black glass might look good.
Or a band of My Little Ponies covering the surface should keep those keys and whisky glasses off.

Potection
Looks like a landslide for no glass and I agree, I also have a beautiful rosewood sideboard and I will say if you have any workmen delivery men in the house cover it or move it, I had a guy in to do some work some how a screwdriver flew out of his hand and traveled some 5 meteres hit the sideboard and left a 1cm chip right in the middle!
Enjoy the sideboard.