According to Pleco:
zháo zhòng: emphasize; attach importance (v) / emphasis (n)
zhuó zhòng: stress; emphasize (v)
Both use 着重 as its characters. The first one lists a noun as well as a verb as its usage but the second one only lists a verb.
According to 网易有道词典, it only lists the latter.
Usually, if the pronunciation is different, the meaning is differen as well. For example,
zháo means touch while
zhe works as a particle, even though both are written as 着.
But in this case the meaning looks the same. So why do two forms exist and which one I should use?