Open Minecraft and go to the world you want
Pause the game
Select Settings or Game Settings
Find the Seed field
Copy the seed shown there
If you are on a server, ask the server owner for the seed
If cheats are enabled, use the command `/seed`
If you are in a single-player world, open the world settings from the main menu to view the seed
If the seed is hidden on a realm or server, use admin tools or ask the host