How to know which IP is in the blacklist? I often use a mobile device to log in to bitcointalk, as you know, mobile devices connect to the internet using 3G - 4G, and often change IPs every time you turn it off.
You can't find out for sure - the closest you could get is to cross reference from the images posted by theymos (linked to in Husna QA's post above), but that would be very inaccurate given that 1 pixel = 256 addresses, and some of the data had been altered for privacy reasons.
The only way to know for sure if an IP has been blacklisted is to register an account from that IP. If it is blacklisted, you won't be able to use the account until paying the evil fee.
Once the evil fee is paid (or if no evil fee was required in the first place), it doesn't matter which IP you connect from - your account will always work (provided you aren't subsequently banned for breaking the rules). If you were to log in to the account you are currently using on mobile, and your IP changed to a blacklisted IP, it wouldn't matter since your account is already active and you would still be able to post normally.