Run
PRAGMA table_info('my_table_name')
find the record that column ‘pk’ is 1, it’s the primary key.
See also:
How to get primary key of a table from PostgreSQL
How to get primary key of a table from MySQL
How to get primary key of a table from SQL Server
How to get primary key of a table from DB2
How to get primary key of a table from Oracle
Some SQLite tools you can try: https://www.withdata.com/sqlite/