One solution is to sum on a conditional expression like so:
select employeeid, historyid,
sum(case when activitytype = 'OPEN' then 1 else 0 end) Opens,
sum(case when activitytype = 'CLICK' then 1 else 0 end) Clicks
from tablename
group by employeeid, historyid;
"Do not seek to follow in the footsteps of the wise. Instead, seek what they sought." - Matsuo Basho