for 1 question, 

I use M-x describe-font, press Enter after mini buffer shows: Font name(default current choice for ASCII chars).

Get the following info:

name (opened by): -DAMA-Ubuntu-normal-normal-normal-*-17-*-*-*-*-0-iso10646-1

       full name: Ubuntu:pixelsize=17:foundry=DAMA:weight=normal:slant=normal:width=normal:scalable=true

            size: 17

          height: 19

 baseline-offset:  0

relative-compose:  0

Also try to evaluate the expression in eshell, get the same result.

~ $ (face-attribute 'default :font)

#<font-object "-DAMA-Ubuntu-normal-normal-normal-*-17-*-*-*-*-0-iso10646-1">

for 2 question, please see the following screenshot, after C-u C-x RET, mini buffer shows C-u C-x RET-