Calculate directional derivative 0f $\phi$ at the point $Q$ in the given direction:
$\phi=\ln\sqrt{x^2+y^2+z^2}$, $Q(a,b,c)$; towards the origin.
I firstly need to find $\operatorname{grad}\phi=\dfrac{1}{x^2+y^2+z^2}(x\mathfrak{i}+y\mathfrak{j}+z\mathfrak{k})$
Then I replace the point $q$ in $\operatorname{grad}\phi$. Then, I do not know how to proceed with the origin.
It seems that you know the right definition of directional derivative. Just note that, here we need a unit vector preferably. So, as the exercise wanted use the following unit vector $$\vec{u}=\frac{\vec{QO}}{|\vec{QO}|}$$