Can we directly upgrade Oracle 12.1 to 19 c or do we need to upgrade 12.1 to 12.2 first and then 19c
The term used by Oracle is "direct upgrade". You have to take into consideration if your database is a multitenant (CDB) database. 

From https://mikedietrichde.com/2018/12/14/premier-support-extension-for-oracle-19c-and-more/ :


  Oracle 12.2.0.1, Oracle 18c and Oracle 19c all together sail under the cover of the “Oracle 12.2 Release Family” and hence have a common support frame


So direct upgrade should be available with the following versions: 11.2.0.3, 11.2.0.4, 12.1.0.1, 12.1.0.2, 12.2.0.1

I'm not adding the MOS support hyperlinks since if you are posting the question here I'm guessing you dont have a MOS account.