A # B means 'A is the brother of B'.

A @ B means 'A is the son of B'.

A & B means 'A is the father of B'.

A % B means 'A is the mother of B'.

If W # Q @ T & Y @ M % K % L, then how is K related to W?

Sister

ATQ, 

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Please note:

  l   ⇒ Vertical line shown "generation gap".

 =  ⇒ Double lines shown "relation of spouse" 

—  ⇒ Horizontal line shown "relation in same generation other than spouse".

     ⇒ Rectangular box shown " Male".

     ⇒ Circular box shown " Female".

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