How to get XYZ url for a specific Scene/Item?

To get the XYZ url, you will need to request it using API Tile Services.

The API Tile Service and Basemap Tile Service make is easy to visualize Planet imagery in desktop or web mapping applications that support either the XYZ or WMTS protocol. These services offer a low-friction way for web developers and GIS analysts to interact with, and derive value from Planet imagery without the need for further image processing.

More Details - https://developers.planet.com/docs/basemaps/tile-services/#api-tile-service 

Here is an example request in Python- 

API Tile Service Request Structure

https://tiles1.planet.com/data/v1/PSScene3Band/20161221_024131_0e19/14/12915/8124.png?api_key={api-key}

API Tile Service Request in Python with Basic HTTP Authentication

import os
# import os module to access enviornmental modules

import requests
from requests.auth import HTTPBasicAuth
# import helper functions to make Basic request to Planet API

PLANET_API_KEY = os.getenv('PL_API_KEY')
# Setup the API Key from the `PL_API_KEY` environment variable

BASE_URL = 'https://tiles{0-3}.planet.com/data/v1/{item_type}/{item_id}/{z}/{x}/{y}.png'

if PLANET_API_KEY is None:
    PLANET_API_KEY = '12345'
# pass in your API key

auth = HTTPBasicAuth(PLANET_API_KEY, '')
# HTTPBasicAuth() wants a username & password; you can pass an empty string for the password

res = requests.get(url=BASE_URL, auth=auth)

print(res.status_code)
# make a request to Tile Services API and test the response