It depends on your existing skill set and what level of commitment you want to give this new part time job. It also depends on when you find you are busiest with sex work.

For example - a part time cleaning job in early morning hours would work alongside day time / evening sex work.

An evening bar / restaurant would work if you tend to do sex work through the day.

A day time shop assistant / office assistant / librarian / insert other would suit if you tend to do evening sex work.

It really all depend which job is going to be the main focus and which is going to be the supplementary. Bare in mind that some industries, particularly bar, restaurant and shop work, tend to be rota'd not very far in advance and they can change your shifts last minute or even cancel your shift / extend your shift last minute. This might conflict with your sex work if you make advance appointments with clients.

It really all depends! There aren't really any jobs that are better suited than others - it just depends on how to intertwine the two.