Adiyen requests to enlighten us on the significance of having Shikhai on the head and is it a must to have Shikhai while doing Sandhyavandanam, Saaligrama Aradhanam and other nitya/naimittika karmams?
Adiyen Ramanuja Dasan

Yes Shikha is must for all Brahmins (not only for Vaishnavas),
When we do the Anga nyasam, Kara nyasam, Kavacham etc. we can find the sentence "Shikayai Aushat" is a kavacham.
And Vedham also compelling Shikai by giving an example as here under:
.... insisting that "Kudumi" is required to do anushtanams.
here is that vedha vaakyam :
"....yathra baana: sampathanti kumaaraavishikaaivaa"
The baaNas (arrows) were fell down wastefully like the Argya theertham of kumaaraas (boys) without shikaa"

Pranamams to NVS swamy. Thanks for confirming that Shikha is indeed essential. Adiyen wants to know if there is any procedure on how to do the Kudumi or have Shikha on the head and excatly where on the head the Shikha should exist. It would be helpful if you give some instructions on this.
Adiyen Ramanuja Dasan

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I yet to know, where the specifications for Sikai is given in Shastras,
but as per practice and experience,
The loose hairs in the forehead and around the head to be removed and shaved thats it.