In the Quote Standard Fields (Setup > Customize > Quotes > Fields) there is no CurrencyIsoCode field. However, when I run the following apex code:
List<Quote> quotes = [SELECT Id, Name, CurrencyIsoCode FROM Quote LIMIT 1];
System.debug('>>> quotes: ' + quotes);
I can see CurrencyIsoCode:
16:55:42:004 VARIABLE_ASSIGNMENT [25]|quotes|[{"Id":"0Q00m000000Cl4KCAS","Name":"Test_20170623","CurrencyIsoCode":"EUR","RecordTypeId":"012610000002iLVAAY"}]|0x4da9e55a
No clue on the CurrencyIsoCode field of the Quote object in this help doc either.