Function for counting opening trades

You're not learning anything by asking for something. You should learn to code and attempt it yourself, then post your attempt here. Then we would assist you and guide where possible. Anyways, here:

int OpenOrdersThisPair(string pair)
  {
   int total=0;
   
   for(int a=OrdersTotal()-1; a>=0; a--)
    {
     if(OrderSelect(a,SELECT_BY_POS,MODE_TRADES))
      if(OrderType()<=1)
       if(OrderSymbol()==pair) total++;
    }
     return(total);
  }