The lowest C note In the stave with the G clef (in the wiki picture) is middle C, MIDI note number 60. The C below A = 440Hz in Equal Temperament..
What it is named, i.e. C3 or C4, C5, etc. will depend upon which system you are using, scientific, Helmholtz or another.
Manufacturers of DAW software tend to use different numbering systems too.