"судовольствием"

Lol, that's really unusual to see a dog who enjoys a bath! браво, 212, for the great videoclip! спасибо.

how can he be comfortable with all that water inside his ear!?

The „у-“ prefix here indicates a purpose.

The „до-“ prefix here means “completely”.

The „воль-“ morph here means “desire”, from the Proto-Indo-European root *welh-, as in the English words “will” and “well”.

The „-ствие“ suffix means “-hood | -ness”.

Compare „дово́льный“=“pleased | satisfied | content | happy”.

Same root as удовлетворить -- "to satisfy" I imagine (used to be удовольствовать), and the suffixes -ствие/-ство tend to conceptualize concrete objects. Can't find anything that goes any further.

In some, but not all contexts. In Russian, you can use "C удовольствием" by itself, in response to someone suggesting/offering something that you will enjoy (e.g. Пошли в кино - Let's go to the movies). I don't think you can just say "gern(e)" here.

С радостью would be with joy.

No, not really.

And "I am satisfied with" is not very accurate translation for "я доволен". "I am pleased with" is more like it.

I am satisfied = я удовлетворен (feel OK with the result)

я доволен - feel better than OK with the result

"С удовольствием" is literally "with pleasure".

Both "С удовольствием" and "With pleasure" are fixed expressions indicating your eagerness (to do something) while "With happiness" is not.

„счастли́вый“ is an adjective, meaning “happy” (‘alegre’); the adverb would be „счастли́во“=“happily” (‘con alegría’).

„с удово́льствием“ is a adverb, meaning “with pleasure” (‘con agrado|gusto’, literally ‘con placer’).