The right one for heaven? That's very uncertain! (5)
I believe the answer is:
risky
'very uncertain' is the definition.
'risky' can be an answer for 'uncertain' (I've seen this in another clue). I am not certain of the 'very' bit.
'the right one for heaven?' is the wordplay.
'the right' becomes 'r' (abbreviation).
'one' becomes 'i' (Roman numeral).
'for' is a charade indicator (letters next to each other).
'heaven?' becomes 'sky' (I've seen this in another clue).
'r'+'i'+'sky'='RISKY'
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for risky that I've seen before include "admitting possibility of unpleasant outcome" , "Having possibility of danger or loss" , "Speculative" , "too adventurous" , "Treacherous" .)