Below is the query to check the ASM diskgroup utilization.
select NAME ,TOTAL_MB/(1024) TOTAL_GB,FREE_MB/1024 FREE_GB,(TOTAL_MB-FREE_MB)/1024 USED_GB,(FREE_MB/TOTAL_MB)*100 FREE_PER from v$asm_diskgroup.
NAME TOTAL_GB FREE_GB USED_GB FREE_PER
------------------------------ ---------- ---------- ---------- ----------
DATA 3000 2058.43359 941.566406 68.6144531
FRA 3000 2756.07031 243.929688 91.8690104