He bought shares by instalments – should he deduct the shares when paying zakaah?

Firstly: 

The one who buys shares with the intention of dealing in them
must pay the zakaah of trade goods at the end of the year, so he should work
out their market value and pay one-quarter of one-tenth. 

The one who buys shares with the intention of keeping them
and benefiting from their profits and not dealing in them, should pay zakaah
on the profits. For more information please see the answer to question no.
69912. 

Secondly: 

If one year has passed, and you still have some instalments
left to pay, you have to pay zakaah on the shares regardless of these
instalments, because a debt does not affect zakaah, according to the more
correct of the two scholarly opinions. This is the view of Imam al-Shaafa’i
(may Allaah have mercy on him). See: al-Majmoo’ (5/317); Nihaayat
al-Muhtaaj (3/133). 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said:
What I think is more correct is that zakaah is obligatory in all cases, even
if he owes a debt that takes his wealth below the nisaab (minimum
threshold), except a debt that is due before the year is up, in which case
he must pay it off, then pay zakaah on what is left after that. End quote
from al-Sharh al-Mumti’ (6/39). 

And Allaah knows best.