Janā literally denotes picked fruit. In janāki, the fruit is figuratively attributed to the beloved. The context does not describe literal fruit; it evokes the sweetness of her affection or closeness.
Al-muʿallal is explained in classical usage through the notion of repeated or successive giving; the related verb ʿallalahu can describe repeated provision of drink. The epithet intensifies the wish for renewed enjoyment.
The first hemistich concerns the rein of travel, the second the fruit of affection. The combination gives the verse both physical movement and emotional desire.