Poke is a slang term with numerous meanings.
This poke is referring to stabbing someone. In L'A Capone's "Intro" song, he raps "If he got them oz., then we poke him." L'A Capone is saying if someone (dealer) has drugs (oz) on him, he'll stab them up for their drugs.
Poke is also a slang which refers to any sexual acts that involves penetration.
Many social networking sites have a poking feature which lets you poke other users. Prior to the birth of social networks, people used to send "poke" as a message to other chats users as a joke to see if they were still active in the chat.