In dynamic block request body, you can use Full Subscriber Data variable, that contains all subscriber’s information:
{
"id": 13245647xxxxxxxxx,
"user_ns": "f3245647xxxxxxxxx",
"page_id": 234564657xxxxxxxx,
"status": "active",
"first_name": "Subscriber",
"last_name": "Lastname",
"name": "Subscriber Lastname",
"gender": "male",
"image": "https://xxxxxxxxx.com/xxxxxx.jpg",
"locale": "en_US",
"language": "English",
"timezone": "UTC-07",
"last_input_text": "Last subscriber's input text",
"subscribed": "2018-07-02T00:00:00+00:00",
"last_interaction": "2018-07-02T00:00:00+00:00",
"last_seen": "2018-07-02T00:00:00+00:00",
"custom_fields": {
"customField": 0.75,
"customDate": "2018-05-31",
"customBool": true,
...
}
}