About pokazivati and pokazati, you are right.
About your sentences:
1. Your sentence absolutely can pass but correct form is: Ne znam pokazuje li joj knjige.
2. Correct.
Now, I assume you'll be asking why is "je" ommited in first sentence. The difference between first and second sentence is tense. While first is in present form, second one is in past and we form past tense with present form of verb "biti" (to be) and main verb in correct form.
Present form of verb "biti" is:
sam (for I)
si (for you)
je (for he/she/it)
smo (for we)
ste (for you - more persons and for polite form singular)
su (for they)
Those above words are short forms of verb "biti".
Longer forms are: jesam / jesi / je/ jesmo / jeste/ jesu
For past tense main verbs end with:
singular: -o/ao (masculine), -la (feminime), -lo (neutral)
plural: -li (masculine), -le (feminime), -la (neutral)
Of yourse, there are some exceptions :)
And some examples for making my answer more understandable (about "je"):
Am I here? - JESAM li ovdje?
Does this work? - Radi li ovo? (here you do not have present form of "biti")
Does it rain? - Pada li kiša?
Did you sleep well? - JESI* li spavAO dobro? --> past tense
* when you ask questions (when verb "biti" is at the beggining of question), you should use longer version
If you need more explanation, just ask.