Salam Spangola, Actually there's a sukun on the letter ب in تِبْن :) I don't know if I got your question right, but تبن as in (hay), indeed has a sukun, same as bint (girl). For me the only way I know of is to enlarge my screen and it works perfectly, otherwise it's nearly impossible to see tashkeel.

As you have said تبن has only a "Kasra" on ت and a "sokoon" on the "Ba" and no "tashkeel on "noon " as when you say the word itself the last letter always been pronounced with "Sokon" but we change that "sokon" while we are speaking Ex: "The horse is eating hay" "الحصان يأكل التبنَ " & "اشتريت تبنًا لحصانى" I bought hay for my horse. I understand why u ask about that as a verb as Build is "بنىَ يبني " and if u wanna ask some1 "Are u building something?" "هل تبنى شيئًا؟" or "If u couldn't build that this year it'd be possible to build it any time else" "ان لم تبن هذا البناء هذه السنة سيكون مستحيلا ان تنهه فى اى وقت آخر" So yes u have to know "Tashkeel" for every single word to read it correctly.. But believe it or not we don't use it anymore except for Quraan U can't read Qura'n without "Tashkeel" U will become more familiar with it in the future Read a lot and listen to natives a lot it'd help a lot too =D

We have only one word made up from this sequence of letters ت ب ن so it would not be confused with any other words , we do not need to put those tiny vowels "tashkeel(s)" to distinguish it. in most case Arabic writing depend on the process of guessing. This happens in English to . there is times when you read "use" with /s/ sound like in "make use of" and other times when it becomes /z/ like "Use the stairs"..