What the name of this coin cell battery and its holder?
That footprint is not for a holder.  It looks like it's meant for a coin cell with solderable leads.  From the "RTC" and the watch crystal, it looks like the battery is for keeping a low power clock running when 5 V isn't supplied on the IIC interface.

I'll guess that a 3 V battery would work fine.  Look around on the a distributor site like Mouser for the largest capacity 3 V leaded coin cell you can find that fits mechanically.  You have considerable leeway for the cell diameter, up to just under 10 mm maximum.  8 mm looks like it would be a comfortable fit.

Panasonic is one supplier of such batteries.  They are not hard to find.