in tanzania it's common to shorten any first person present tense verb to cut out the ni- prefix. "nasoma" would be common here too as you said it is in kenya.
While I haven't heard people say "nijua", I have heard "najua" to mean "ninajua."
"tuende" or "twende" is a separate thing though. this is a polite command (as evidenced by the "e" at the end, rather than an "a" as in "kwenda), not an abbreviated present tense verb.