A good substitute for pineapple juice is mango juice.
Mango juice has a similar tropical flavor profile to pineapple juice and the option to add a bit of lime juice to replicate the acidity of pineapple juice.
Other substitutes for pineapple juice are a blend of apple juice and lemon juice, a combination of passion fruit and guava juice or even orange juice.
If the recipe relies heavily on the sweetness of pineapple, then you can opt for a fruit juice with similar sweetness such as mango juice.
If you want to mimic the pineapple's slight tartness, you can consider adding a splash of citrus juice such as lime juice or lemon juice to the substitute.
And depending on the dish you may want to juice a fruit juice that also complements the other flavors in the recipe.
Other substitutes for pineapple juice are.
A blend of tropical fruit juices.
Lychee juice.
Apple juice mixed with a bit of lemon juice.
Grapefruit juice although it has a stronger flavor.
Or canned mandarin orange juice.