Interesting terminology. While it is in attributive position, it still functions as predicate.
ὁ δεινὸς (pred.) λεγόμενος γεωργός = ὁ γεωργός ὁ δεινὸς λεγόμενος = ...ὃ δεινὸς λέγεται
This is the complete sentence:
ἐπεὶ δέ με καθ᾽ ἓν ἕκαστον ἐπεχείρησας ἐρωτᾶν, ἀποκρίνομαί σοι,
ὡς σὺ φῄς, ἅπερ σὺ γιγνώσκεις ὁ δεινὸς λεγόμενος γεωργός.
But now that you have undertaken to question me in particular,
my answers, you tell me, agree exactly with the views of
a farmer so famous for his skill as yourself!
-- William Heinemann, 1979
This is why it pays to check the complete quote and not a fragmented portion a grammarian has
offered as an example to his/her posited findings.
ὁ δεινὸς λεγόμενος γεωργός appears to be in apposition to σὺ:
...I answer you -- as you say -- exactly what you, a farmer known for his skill, have come to know.