Ingredients

• Pickling salt
• 2 lbs skinless, boneless salmon fillets
• Apple cider or white vinegar
• Sugar
• Pickling spice
• 2 white onions
• 1 quart size glass jar

Process

• Salt the fish, top and bottom, in a glass or plastic container. Cover and refrigerate 24 hours.
• Make pickling liquid: combine 2 parts vinegar to 1 part sugar and 1T pickling spice in a saucepan over low heat. Simmer 5 minutes, stirring occasionally. Refrigerate until cool.
• Remove fillets from salt and rinse in cold water. Discard salt. Rinse container, add cold water until covered. After 8-10 hours, remove fillets from water, pat dry, and cut into 1 inch cubes. 
• Layer  onions and salmon in quart jar. Pour pickling liquid over fish and onions as layers build. Seal and refrigerate for 72 hours before eating. Flavor will intensify with more time. Shelf life is about 1 month. Label the jar with date.

Source: https://aksalmonsisters.com/blogs/news/pickled-salmon-recipe-1