void daytext(){
 wk = (wk + 1) % 7; //What does this do?

the above code does this:
"the remainder of (wk + 1) divided by 7 equals wk"


here's the code to get day of week, tweak it to suit your needs:



GregorianCalendar gcal = new GregorianCalendar();

void setup(){
size(50,50);
frameRate(30);
}

void draw(){
background(0);

int week = gcal.getActualMaximum(Calendar.DAY_OF_WEEK);

   println("Day of week: " + week);

   int first = gcal.getFirstDayOfWeek() ;

   switch(first){
     case 1:
       println("Sunday");
       break;
     case 2:
       println("Monday");
     break;
     case 3:
       println("Tuesday");
       break;
     case 4:
      println("Wednesday");
     break;
     case 5:
       println("Thrusday");
     break;      
     case 6:
       println("Friday");
     break;
     case 7:
       println("Saturday");
     break;  
 }
}