Is there a particular dua for a parent that passed away?

Salam alaikum! Is there a particular dua for a parent that passed away? My father died few years ago and I don't know what to do so that Allah grant him jannah.. Is there a particular moment to do so? Or a particular day? Something particular to say? I'm really desperate to do something but i don't know what. And do you know if the dua reaches the person? Can they hear it ? Or know that someone on earth is praying for them ? Thank you for your replies

Walaikum As’salaam,

The Noble Qu’ran | Surah Al-Baqarah [2:156]
"Inna lillahi wa inna ilayhi raji’un"
"Indeed we belong to Allah, and indeed to Him we will return."

Here is a Dua from The Noble Qur’an that you can recite for your father, Insha’Allah:

The Noble Qur’an | Surah Al-‘Isra [17:24]
“O my Lord! have compassion on them, as they brought me up (when I was) little.”

Prophet Muhammad (Sallahu Alai wasallam) said:

“When the son of Adam dies his actions come to an end except three things, a continuing charity or knowledge which gives benefit or a pious child who prays for him”[Sahih Muslim]

Therefore, pray for your father, make dua to Allah (SWT) to forgive all his sins and grant him Jannat-ul-Firdous, Insha’Allah.
In another Hadith a man asked the Prophet (Sallallahu Alaihi wasallam):

"My mother had a sudden death, and did not have chance to bequeath anything. Had she been able to do, I think that she would have given sadaqah (charity). Would she or I get any rewards if I give sadaqah on her behalf?"
He (Sallallahu Alaihi wasallam) replied:
"Yes! So give sadaqah on her behalf."
[Al-Bukhari, Muslim and others]

As per the Hadith, sadaqah (charity) given with the intention that Allah (SWT) rewards your father is also an excellent way for your father to earn rewards even after he has passed away, Insha’Allah.
Please kindly note: I’m not a scholar or one with extensive Islamic knowledge so I can only advise you based on the research I’ve found and personal experience. I highly encourage you to further research the matter and seek advice from others  with more reliable Islamic knowledge (i.e. a scholar or imam, etc) than myself. c:
Therefore, in terms of them knowing/hearing if you pray for them, I’m honestly not sure.  I have heard that they know when someone is praying for them, however, I’m not 100% sure and do not wish to give you incorrect information. c:
And so, I highly encourage you ask someone with more Islamic knowledge, such as an Imam at your local mosque, or an Islamic scholar, etc, Insha’Allah they’ll be able to answer your question. :)
I hope I was able to help at least a bit Insha’Allah. May Allah (SWT) bless your father with the highest rank in Jannah, may He forgive all his sins and may He bless you and your family, Ameen! :)