How to transfer REST request data in another Request using Property transfer ?

 Here , 3 REST request are present Register, Log in, Update Profile.

 I want to transfer Register json request "email" value in Login request  using property transfer.

  this is Register JSON request below ---

 {
"rg":

    {
"appv": "15.9",
"dtype": "1",
"title": "003",
"firstName": "erer",
"surname": "taterea",
"mobilePhone": "2222222",
"password": "12345678",
"cpassword": "12345678",
"postCode": "st44ph",
"address1": "uk",
"email": "test@test.com",
    }
} 

 How to set Source path for Email in Property transfer ?  Please reply.