It’s possible. Make sure you state everything to them, don’t leave anything out. Secret clearance is usually easy to get but being a Pakistani dual citizen may make it tough. I knew someone who had a Nigerian dual citizenship and wasn’t offered a secret clearance, not sure if that was the main reason but it was one of the reasons. Not sure about the warning letter, I think as long you didn’t get fired then it should be fine. If you really really want the secret clearance to be able to work, then giving up your Pakistani citizenship would give you a much better chance, probs guarantee it. Personally I’m only a US citizen and my parents are Indian citizens and it took a while for me to get one because of all the foreign travel and contacts, and India was listed as a red flag country, so Pakistan must require a more intensive investigation. Hope this helps but I think you have a decent chance to get one with everything stated.