Younis followed up a match-winning double century in the first Test with an unbeaten 52 as Pakistan reached 163 for three at the close of play in reply to Zimbabwe's first innings total of 294.
When he reached 50 for the 49th time in Test cricket Younis became the fourth Pakistan batsman to reach 7000 runs in Tests.
Batsmen of both sides played cautiously on a slow pitch. Only five wickets fell in the day, while 222 runs were scored.
Younis and fellow veteran Misbah-ul-Haq will resume on Thursday, after putting on 67 for the fourth wicket. They came together soon after tea when opening batsman Khurram Manzoor was run out for 51.
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Younis faced 127 balls and hit six fours, while Misbah made 27 not out off 88 deliveries.
Manzoor, who was recalled for the Zimbabwe series after more than three years out of the Test team, survived confident appeals for a catch behind and leg before wicket early in his innings.
Pakistan endured a frustrating morning as their bowlers struggled to dislodge the Zimbabwe tail.