Most Emerald journals operate article-level publishing (ALP), whereby articles are processed for EarlyCite publication immediately following acceptance. EarlyCite articles are later compiled into the next available journal issue based on date of copyright assignment
If the citation includes 'Ahead of Print' in the details, this means that the article has been published as Earlycite and has yet to be assigned to a journal issue:
In this instance, you should cite the article without the volume and issue details.