I'm replacing heater control valve which hose does it go in ? how can I tell ?
Does not matter. The valve is like a Doorway and the hoses are pipes that allow the coolant to flow when the doorway(called a GATE) is open, When the"GATE" is closed no coolant flows.
Your best bet would be to take note of which hose came off which port during removal of the old core, and tag them so you can get them back where they belong later. Taking pictures during disassembly helps a lot, too. It doesn't have to be Mapplethorpe, just clear enough that you can get the routing right. Tagging doesn't have to be any big deal, just a quick A B C with a white marker ought to suffice.
If it's too late for that then your next best bet would be to check the factory service manual, which should spell out the hose routing pretty clearly.
If you don't have a FSM or even a Haynes or Chilton (I recommend Haynes) manual, then try running the hose that comes off the hottest part of the water circuit to the heater's input side. If you know what direction your water flows in the cooling system then this is a pretty straightforward prospect but you haven't told us what kind of car we're talking about.
Replace them one by one. Again one by one.
consult diagram in owner's or service manual
The new one goes in where the old one came out of. Take digital photo's as you disassemble anything.