The available columns for any given table are fetched from a system table called "sys_tablecolumns". A specific table name is provided in the WHERE criteria to restrict the table from which the column information is fetched:

import cdata.reckonaccountshosted as mod
conn = mod.connect("SubscriptionKey=test;CountryVersion=2021.R2.AU;CompanyFile=Q:/CData Software.QBW;User=test;Password=test;InitiateOAuth=GETANDREFRESH;CallbackURL=http://localhost:33333;OAuthClientId=MyOAuthClientID;OAuthClientSecret=MyOAuthClientSecret;")
cur = conn.cursor()
cmd = "SELECT * FROM sys_tablecolumns WHERE TableName = 'Customers'"
cur.execute(cmd)
rs = cur.fetchall()
for row in rs:
	print(row)