appending string to char and vice versa
solved it. was simple actually. dont know how to do it with chars, but with strings there is the addition operator.
So i converted both to string and used the + operator.

char clat[10 + 20 + 1] = "Latitude/Longitude: ";
char clng[10 + 1];
String string1, string2, finalstr;


and inside the loop:

dtostrf(gps.location.lat(), 10, 6, clat+20);
dtostrf(gps.location.lng(), 10, 6, clng);
string1 = String(clat);
string2 = String(clng);
finalstr = string1 + string2;


Maybe that was too much work?
If you have any smarter alternatives, please provide!