How to use PIVOT here?
To be honest, for such need, I would not use pivot, I would simply:

select XPK, 'Total_count', First_count + Second_count
from my_table
union
select XPK, 'Total_amount', First_amount + Second_amount
from my_table


If you really want to use pivot you can try:

select XPK, kpi, total
from (
select XPK,  First_count + Second_count as Total_count, First_amount + Second_amount as Total_amount
from my_table
) t
unpivot (total for kpi in(Total_count, Total_amount)) tt


But maybe your problem is more complex than what you described....