It depends how you define it, many different branches..
- Under the RH there is a branch of $\text{arg } \zeta(s)$ which is continuous on $\Re(s)\in (1/2,1)$,
letting $$\text{arg }\zeta(1/2+it)=\lim_{\epsilon\to 0^+}\text{arg }\zeta(1/2+it+\epsilon)$$ then yes there is a $+ k\pi$ jump at each non-trivial zero of multiplicity $k$.
- If you don't believe in the RH then there is a branch of $\text{arg } \zeta(s)$ continuous on $\Re(s) > 1$ and on every horizontal strip without zeros,
in which case $\lim_{\epsilon\to 0^+}\text{arg }\zeta(1/2+it+\epsilon)$ has a $+ k\pi$ jump at each zero of multiplicity $k$ on $\Re(s)=1/2$ and a $+2k\pi$ jump at each $t$ such that there are $k$ zeros (counted with multiplicity) on $\Im(s)=t,\Re(s) > 1/2$.