Get Job step run for all jobs and job steps using TSQL
This should get you close, if NULL for ProxyName then it's using the SQL Server Agent credentials.  

USE msdb

SELECT J.job_id
    , J.name
    , S.step_name
    , S.step_id 
    , P.name AS ProxyName
    , SP.name AS CredentialUserName
    , SP.type_desc AS CredentialUserType
FROM msdb.dbo.sysjobs J
    INNER JOIN msdb.dbo.sysjobsteps S ON S.job_id = J.job_id 
    LEFT OUTER JOIN msdb.dbo.sysproxies P ON P.proxy_id = S.proxy_id
    LEFT OUTER JOIN sys.server_principals SP ON SP.sid = P.user_sid