Hm, you’re right about the apostrophe. Toaq and Eberban use the apostrophe for the glottal stop. Lojban uses the period. What other glyph do you suggest? x? Of the letters in the English alphabet, the following are not used by Sekko: j f v w x.
j f v w x
Yeah, x seems the most appropriate candidate. It sufficiently rare in English to not trip people up too much, from a cursory glance at Wikipedia it’s at least used for that purpose in Pirahã, and it even looks like a little pictographic “stop” symbol.
Edit: Oh, apologies, I completely misunderstood the part where “ņ” was actually written with the letter “q”. Nevermind that part!