My thick Germanic based tongue betrays me how is this pronounced?
In what author are you seeing this?
Generally, these two vowels together are not regarded as producing a diphthong. So, they are pronounced separately: eh-oh, that is, [ɛ.ɔ] in IPA.
In Erasmian. In the reconstructed pronunciation it will be [eo], as in θεός.
I asked about author because there’s some funkiness in Ionic orthography on εο/ευ in a contraction. It probably won’t matter except in certain editions of certain authors, in particular West’s Homer.