$$y=ln(lg(x)) - lg(ln(x))\\ I:\\ y_1=ln(lg(x))\\ z=lg(x)\\ \frac{dz}{dy}=\frac{1}{x\cdot ln(10)}\\ y_1=ln(z)\\ \frac{dy_1}{dz}=\frac{1}{z}\\ ⇒y_1=\frac{dy_1}{dz}\cdot\frac{dz}{dx}=\frac{1}{lg(x)}\cdot\frac{1}{x\cdot ln(10)}\\$$
$$II:\\ y_2=lg(ln(x))\\ z=ln(x)\\ \frac{dz}{dx}=\frac{1}{x}\\ y_2=lg(z)\\ \frac{dy_2}{dz}=\frac{1}{z\cdot ln(10)}\\ ⇒y_2=\frac{1}{ln(x)\cdot ln(10)}\cdot\frac{1}{x}\\ $$
$$y'=y_1'-y_2'\\ y'=\frac{1}{lg(x)}\cdot\frac{1}{x\cdot ln(10)}-\frac{1}{ln(x)\cdot ln(10)}\cdot\frac{1}{x}\\ y'=\frac{1}{ln(10)}\Bigl[\frac{1}{lg(x)\cdot x}-\frac{1}{ln(x)\cdot x}\Bigr]$$