IUPAC nomenclature of protonated aminoacids
Interestingly, Ammonium salts come above acids in the seniority table for functional groups (Reference: Wikipedia). Also, the ion in question has an alkyl group attached to it, which makes the suffix aminium rather than the commonly used ammonium. (Reference: Gold Book, Wikipedia)  This means that the correct name of the compound is 6-carboxyhexan-1-aminium. This was also checked with ChemDraw online, as mentioned in the comments.