One common theme is the exploration of power dynamics. Given Joseph's strong stand abilities and Alessi's unique powers, many fanfics play around with how they interact in terms of power. For example, who would overpower the other in different situations.
There's also 'Alessi's Encounter with Joseph Joestar' which focuses more on a specific event where their paths cross. The author does a great job of capturing the essence of both characters, with detailed descriptions and exciting dialogue. This fanfic really brings their interaction to life in a way that stays true to the original series.
There's no way to really tell if it's common specifically for someone named Jojo. However, in general, reading fanfiction is a popular activity among fans of many different franchises. The Jojo series has a large and dedicated fan base, so it's likely that there are fans named Jojo who partake in reading fanfiction, but we can't say for sure how common it is without more data.
Perhaps this Jojo is interested in exploring different interpretations and stories within the Jojo universe that fans have come up with. Fanfiction often takes the existing characters, settings, etc. from the original Jojo series and creates new and unique storylines. So, this Jojo might be a big fan of the series and wants to see what other fans have imagined.
It depends. Maybe there are some telltale signs or elements that suggest it's a JoJo reference fanfic, but without specific context, it's hard to say for sure.