Whenever a verb comes before a postposition (of, to, from, at, on, with etc.), the end ā vowel drops so the verb ends in just n or ṇ respectively. Consider the following examples where the prepositions and verbs are highlighted.
ਇਹ ਕੰਮ ਕਰਨਾ ਚਾਹੀਦਾ ਹੈ
ih kamm karanā chāhīdā hae
This work ought to be done
ih kamm karanā chāhīdā hae
This work ought to be done
ਇਹ ਕੰਮ ਕਰਨ ਦਾ ਕੀ ਫਾਇਦਾ ਹੈ?
ih kamm karan dā kī phāidā hae?
What was the point of doing this work?
ih kamm karan dā kī phāidā hae?
What was the point of doing this work?
karanā (to do) becomes karan in the second sentence because it is immediately followed by the postposition dā (of)
ਇਹ ਸਮਝਣਾ ਬਹੁਤ ਔਖਾ ਹੈ
ih samajhaṇā bahut aukhā hae
It’s very difficult to understand
ih samajhaṇā bahut aukhā hae
It’s very difficult to understand
ਇਹ ਸਮਝਣ ਲਈ ਧਿਆਨ ਨਾਲ ਪੜ੍ਹਨਾ ਪੈਂਦਾ ਹੈ
ih samajhaṇ laī dhiān nāl paṛhanā paendā hae
To understand it, one has to read carefully (lit. For understanding, one has to read with care)
ih samajhaṇ laī dhiān nāl paṛhanā paendā hae
To understand it, one has to read carefully (lit. For understanding, one has to read with care)
samajhaṇā (to understand) becomes samajhaṇ in the second sentence because it is immediately followed by the postposition laī (for)
ਮੈਂ ਕੁੱਝ ਕਹਿਣਾ ਚਾਹੁੰਦਾ ਹਾਂ
mae(n) kujjh kahiṇā chāhunddā hā(n)
I want to say something
mae(n) kujjh kahiṇā chāhunddā hā(n)
I want to say something
ਮੇਰੇ ਕਹਿਣ ਦਾ ਮਤਲਬ ਇਹ ਨਹੀਂ ਸੀ
mērē kahiṇ dā matalab ih nahī(n) sī
That’s not what I meant (lit. This was not the meaning of my saying this)
mērē kahiṇ dā matalab ih nahī(n) sī
That’s not what I meant (lit. This was not the meaning of my saying this)
kahiṇā (to say) become kahiṇ in the second sentence because it is immediately followed by the postposition dā (of)