Can we use sql server 2016 with service pack 2 for SharePoint 2019?
As a short answer, Yes SharePoint 2019 supports SQL Server 2016 with SP2.
The Minimum requirements for a database server in a farm One of the following:
Microsoft SQL Server 2016 RTM Standard or Enterprise Editions
Microsoft SQL Server 2017 RTM Standard or Enterprise Editions for Windows
Note: SQL Server products and all future public updates are supported through the SQL Server product lifecycle that means SQL Server 2016 with SP2 is supported.
Yes, you can use SQL 2016 or 2017. SharePoint always supports subsequent patches to the base supported version of SQL.