Geo.WKB.encode

You're seeing just the function encode, go back to Geo.WKB module for more information.
Link to this function

encode(geom, endian \\ :xdr)

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Specs

encode(binary(), Geo.endian()) :: {:ok, binary()} | {:error, Exception.t()}

Takes a Geometry and returns a WKB string. The endian decides what the byte order will be.