I am replacing my current 3 way switch with a smart 3 way switch, how do I know which of these wires is the load and which is the line wire? Thanks in advance
Most often, load is at the top, line is at the bottom. This seems to be your case since you have the black terminal at the bottom.
If it is wired correctly, the wire attached to the BLACK screw will be your hot, or line wire. Either of the other wires will go to the load, but will depend on the position of the other switch. TO BE SAFE, use a voltmeter to determine which wire is your hot wire. The hot wire will always have voltage, the other two (load) will read voltage or no voltage depending on the position of the switch. Unless you rewire your “other” switch position, the load wire will only be connected to the load in one position and not connected in the other position. 
Thanks for your help, I thought the black screw was the hot / line wire but just wanted to be sure. One more question this switch says a neutral wire is required but my current switch does not have one?
Your current switch will not have a neutral wire. Can’t tell from your picture, but in the box there are probably several white wires twisted and connected together with a wire nut. That would be your neutral wire.
There are two white wires going in to the red wire nut? Should I run the neutral there? There are four different switches in this wall plate.
Those are probably neutral wires, but not necessarily on the same circuit as your switch.
All neutral wires terminate at the same point in your main power panel, but the Line and Neutral for any device should be on the same circuit. Too hard to tell from pictures. If you can trace the HOT wire on your switch (the black screw) back to where it emerges from a romex cable or a conduit, you should be able to find the Neutral (white) wire associated with it. I’m assuming you are working on the primary switch that routes to your main panel and not the secondary switch that connects to the load.
Thanks for your help, I got it finished
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