The English used in online ads by nursing recruitment agencies and their Italian members sometimes leaves a lot to be desired. Have a look at these two screenshots:
As you can see, the spelling *(pre) registred nurse is incorrect. It ought to be (pre-)registered nurse of course. The agency nurse who published these ads constantly misspells this common expression in her Facebook postings about the level of English needed to be able to work as a health care professional in the UK. This implies that she not only writes registered nurse incorrectly but that she also probably pronounces it in the wrong way. This is sad, as one would expect an Italian nurse recruiter to speak very good English and especially to know how to spell (and pronounce) the noun which refers to their occupation.
Pronouncing registered ˈreʤɪstrɪd/ˈreʤɪstred or even reˈʤɪstrɪd/reˈʤɪstred is not unusual among native speakers of Italian. This is because Italian has a noun, registro, ɾeˈʤistɾɔ/ɾeˈʤistɾo, which translates the English register and is always stressed on the second syllable, and a verb, registrare, ɾeʤiˈstɾaɾe, which, like the former, contains the cluster /-str-/. Add to this influence the fact that the pronunciation of the -ed ending of the simple past and past participle of English regular verbs often trips up students and you can see why we get the four non-native variants I listed at the beginning of the paragraph.
Register is ˈreʤɪstə/ˈreʤəstə in General British (GB) and ˈreʤɪst(ə)r/ˈreʤəst(ə)r in General American (GA). As you know, in GB a written r is pronounced only when a vowel sound follows, whereas in GA all written r's are normally pronounced. (For further info, have a look at this excellent post by the phonetician Geoff Lindsey.) As far as the -ed ending goes, it is pronounced d both after a vowel sound (GB ˈreʤɪstəd/ˈreʤəstəd) and after all voiced consonant sounds, except d itself (GA ˈreʤɪst(ə)rd/ˈreʤəst(ə)rd). See here.
Registered nurse is a compound characterised by main stress on the second element: thus ˌregistered ˈnurse. Its common abbreviation is RN.