Exegesis:

proselthontes de tines tōn Saddoukaiōn ‘some of the Sadducees came (to him).’

Saddoukaios ‘Sadducee,’ i.e. a member of the religious group called Sadducees.

hoi antilegontes anastasin mē einai ‘who deny that there is a resurrection,’ qualifying the entire group of Sadducees, not the few of them who came to Jesus. For antilegō cf. on 2.34; here it is construed with mē and infinitive to indicate that which is denied. anastasis (cf. on 2.34) refers here and in vv. 33, 35, 36 to the eschatological resurrection.

(V. 28a) epērōtēsan ‘(they) asked.’ As in v. 21f the actual question is preceded by two statements, i.e. of the principle involved (v. 28b), and of the case (vv. 29-32).

Translation:

Sadducees, or, ‘Sadducee men,’ ‘members of the (priestly) party/group of the Sadducees,’ ‘Jews called Sadducees.’ In transliteration the c may become s or k; the latter is preferable where possible.

That there is no resurrection, or ‘that the dead do not rise, or, come to life again,’ etc., cf. on 14.14.

(V. 28a) They asked him a question, saying, or “they set him a problem” (The Four Gospels – a New Translation), or simply, ‘they said to him,’ cf. on “they asked him” in v. 21. In the latter case v. 33 may have to be introduced by, ‘then they asked him.’