How to script alerts in SQL Server?
I was able to get all the properties scripted out.


Open SSMS
Right click on the job
Click properties
Use script button on the top


I created a test job with many features.





This is what I get when I scripted out.  

USE [msdb]
GO
EXEC msdb.dbo.sp_update_alert @name=N'Blocked Tasks &gt; 5', 
        @message_id=0, 
        @severity=0, 
        @enabled=1, 
        @delay_between_responses=183, 
        @include_event_description_in=3, 
        @database_name=N'', 
        @notification_message=N'This is a test', 
        @event_description_keyword=N'', 
        @performance_condition=N'Workload Group Stats|Blocked tasks|default|&gt;|5', 
        @wmi_namespace=N'', 
        @wmi_query=N'', 
        @job_id=N'b97f9d4d-a22d-4745-9d19-9fadd168b4b1'
GO
EXEC msdb.dbo.sp_update_notification 
      @alert_name=N'Blocked Tasks &gt; 5', 
      @operator_name=N'sysadmin', 
      @notification_method = 1
GO


I ran an extended event trace to see what get called. I changed the select statement to select * to see all the values.

EXEC Sp_executesql 
N'  create table #tmp_sp_help_alert  (id int null, name nvarchar(128) null,  event_source nvarchar(100) null, event_category_id int null, event_id int null, message_id int null,  severity int null, enabled tinyint null, delay_between_responses int null, last_occurrence_date int null, last_occurrence_time int null, last_response_date int null, last_response_time int null, notification_message nvarchar(512) null, include_event_description tinyint null, database_name nvarchar(128) null, event_description_keyword nvarchar(100) null, occurrence_count int null, count_reset_date int null, count_reset_time int null, job_id uniqueidentifier null, job_name nvarchar(128) null, has_notification int null, flags int null, performance_condition nvarchar(512) null, category_name nvarchar(128) null,  wmi_namespace nvarchar(max) null,  wmi_query nvarchar(max) null, type int null)   insert into #tmp_sp_help_alert exec msdb.dbo.sp_help_alert         



SELECT * FROM #tmp_sp_help_alert AS tsha WHERE (tsha.name=@_msparam_0)   drop 
  table #tmp_sp_help_alert', 
    N'@_msparam_0 nvarchar(4000)', 
    @_msparam_0=N'Blocked Tasks &gt; 5'