PREFIX ex: <http://a.example>
PREFIX sx: <http://www.w3.org/ns/shex#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>

[] a sx:Schema ; sx:shapes (<http://a.example/S>) .

<http://a.example/S> a sx:ShapeDecl ; sx:shapeExpr [ a sx:Shape ;
  sx:expression
    [ a sx:EachOf ;
      sx:expressions (
        [ a sx:TripleConstraint ; sx:predicate <http://a.example/a> ]
        [ a sx:TripleConstraint ; sx:predicate <http://a.example/b> ]
      ) ;
    ] ] .