Try the Commands Troubleshooting and Help page if you get stuff with server errors.
Minecraft Dolphin NBT Data Tags
Using the summon command to spawn in a minecraft dolphin is simple, take the command and enter into chat and presto you have a dolphin. Dolphins can not be tamed or bred. Dolphins can be summoned with position coordinates to lead players to treasure.
How to summon a dolphin that will lead you to treasure
Dolphins require several nbt data tags for them to lead players to treasure. The CanFindTreasure:1 is the most important, but you'll also require a destination for that treasure. Use TreasurePosX ,TreasurePosY, TreasurePosZ to set your own position in world. Make sure it's in water somewhere the dolphin can actually get too.
/summon minecraft:dolphin ~ ~ ~ {CanFindTreasure:1,TreasurePosX:200,TreasurePosY:50,TreasurePosZ:200}Suggestions or found a bug
Leave me a comment/like on:Minecraft Versions Permalinks
If you're looking for a particular summon mob generator you can link to these specific versions of the command generator.