Seek out the priest
From Create Your Own Story
You find the Sigmarite priest of Sartosa in his office, counting some coins. He is tanned and strongly-built, and he sports many battle scars. Though middle-aged, he still looks fit. This is probably a man with an adventurous background, just like everyone in this city. His thuggish appearance belies his nature: he turns out to be a gentle and courteous man, who greets you with a meal and a foaming tankard of ale.
"We do not get many visitors," he tells you. "Most men around here prefer the company of women of questionable virtue over that of priests and monks. I was myself a pirate in my youth, and I must say I cannot blame them. How may I help you, my good friend?"
This is obviously a man who has been here for a while and knows a lot. You can ask him how the city is going these days, or useful tips for survival in Sartosa. If you feel you can trust him, you can tell him about the shipwreck and your amnesia. If you do not want to talk with him, you can find something else to do in the temple of Sigmar.