All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
As far as we know, there is no evidence about a supplication called the supplication of ‘Jawshan Alkabeer’, or the supplication of ‘As-Saheefah as-sajjaadiyyah’. As regards the supplication of Kumayl, if you mean the supplication that is attributed to Al-Khadr which is reported by Kameel Ibn Ziyaad from Ali then this supplication is reported in a Prophetic narration but it was classified by some scholars, like Ibn Hajar and others as a Dha’eef (weak) narration.
We advise our Muslim brothers to rely on confirmed and authentic Prophetic supplications from the Prophet which are reported in reliable, authentic and well-known books of Sunnah, like Al-Bukhari, Muslim, Abu Daawood, At-Tirmithi, An-Nasaa`ee, and other books of Prophetic narrations.
Indeed, some scholars edited books whereby they mentioned the Prophetic narrations about the supplications and legislated mention of Allaah, and we advise the brother to buy them, the best among which is ‘Al-Kalim At-Tayyib’ which is authored by Imaam Ibn Taymiyyah .
Finally, we warn you against the supplications that are reported in books of innovators and which have no authentic source. In general, these supplications are not free from prohibitions, like innovated kinds of Tawassul (seeking nearness to Allaah by virtue of someone or something), or seeking the help of other than Allaah, or dispraised exaggeration in praising the pious people.
Allaah Knows best.