If I am reading an Attic Greek text with modern Greek pronunciation, how do I read the iota subscripts? Do I ignore them like in the restored pronunciation? Or do I read them as /i/ sound like any other cases where iota appears?
I am not a speaker of modern Greek, but I suspect you would just ignore them. (as far as I know) all long vowels and diphthongs are completely gone from modern Greek, so ο, ω, and ῳ are all pronounced the same, [o]. Long diphthongs (ῳ, ῃ, ᾳ)stopped being pronounced by anybody a long, long time ago (2000+ years) so I doubt they would be pronounced by a modern speaker.
That being said, sometimes I still pronounce them when I’m learning words or paradigms, just so I remember that they are there (it’s not ‘historically accurate’ but it helps me as a learner)
The iota subscript was pronounced in [Attic] Greek until the 2nd century BC, after which is was not pronounced. (Severe and probably misleading simplification of Threatte’s inscriptional evidence [for Attic Greek] there.) Modern Greek does not pronounce it. Nor did Byzantine Greek.
Allen mostly follows Threatte in his discussion, but adds the following quote from Dionysius Thrax:
Περισπωμένων δὲ ῥημάτων συζυγίαι εἰσὶ τρεῖς…ἡ δὲ δευτέρα διὰ τῆς ᾳ διφθόνγγου, προσγραφομένου τοῦ ι, μὴ συνεκφωνουένου δέ, οἷον βοῶ βοᾷς βοᾷ.
So in the 2nd century B.C., when this is written, Thrax is describing the different kinds of contracted verbs, which he calls “perispomenon” verbs, and says that although the ι is added graphically to the ᾳ contraction, it is not “pronounced together” with the α. (I copied and pasted from TLG, but I suppose he scribbled all this out with “αι” not “ᾳ”.)