[MLLEMX31]

What is the pre-shared key for wi-fi?
Is this my router security code?

[dx169]

That is the password that you or someone in the house should have set when they set up the router. If you do not have it ask whoever set the password.

[CipherDias]

Typically it will be on a sticker on the underside of your Wi-Fi Router and also supplied in the paperwork given to you by your internet provider

[Branta]

Typically it will be on a sticker on the underside of your Wi-Fi Router and also supplied in the paperwork given to you by your internet provider

If it is... it should be changed asap to a key of the user's choice. Leaving security keys and passwords on the manufacturer's default is a Bad Idea. Typically the same default is used for every device supplied, which makes them pretty easy to crack.