Your mountains are covering the text (as they should). So you need to write your text above the highest peak, so that it is seen. Use text(x,y,z,'My text here), and make sure the "z" value is high enough, i.e. bigger than the immediate ground under the text.
[X,Y,Z] = peaks(30);
surfl(X,Y,Z)
colormap gray
shading interp
view(0,90)
hold on
longLow = -1; latLow = 0.5; % will be partially covered
longHi = 0; latHi = 1.5; % will be totally covered
plot(longLow, latLow);
h1 = text(longLow,latLow,11,'textLo'); % altitude of z=11 is above highest mountain
h2 = text(longHi,latHi,11,'textHi');
hold off
