Question regarding German

Hi

How can I formulate “My father’s friend’s son”

der Sohn des Freundes meines Vaters or “mein Vaters Freunds Sohn”(??)

I look forward to your feedback

der Sohn meines Vaters Freund

You had it right the first time: “Der Sohn des Freundes meines Vaters”.
Technically correct but not used because it sounds weird would be “Meines Vaters Freundes Sohn.”

MrDibble, I am afraid your suggestion is maybe possible following the strict rules, but no German would ever say it either, because it would be too hard to put the inflection clear enough to distinguish between “my fathers son” and “my fathers friends son”.

I wonder how a conversation would go with that mouthful. Germans would probably break it up into something like:

Wer ist denn das in Foto?
Das da ist der Sohn des Freundes meines Vaters or "Du kennst ja mein Vaters Freund…Das ist der/sein Sohn/Das ist der Sohn von meinem Vaters Freund

I believe in a casual conversation I would rather use a construction that avoids the usage of a double genitive:
“Das ist der Sohn von einem Freund meines Vaters”

I was expecting German to have a way of making a single, long compound word for it.

I have to nitpick here, but you’re willing to learn the language correctly, so I think nitpicking is ok:
*Wer ist denn das in Foto? *

is slightly wrong because of a missing article, in this case the dative:

Wer ist denn das in dem Foto? or with the contraction of in + dem: *Wer ist denn das im Foto?
*
Du kennst ja mein Vaters Freund

is the genetive, so it should be

Du kennst ja meines Vaters Freund.

Das ist der Sohn von meinem Vaters Freund is just plain wrong on more than one level.

Thanks EinsteinsHund. Very helpful. Thank you all.