His best shot would be going after the Time Gem first, but given what Rip's been able to do via time travel without outside amps, Thanos wouldn't have a chance in hell of getting it from him.
I don't see Thanos using the space gem anywhere near
enough to procure the other gems and since we are assuming
that Thanos can use the gem to their compoets definition
Which he never displayed or anyone else has for that matter
than can we assume that the others will also which would
mean that he wouldn't get a single gem in the first place
or even if he did get the space gem which is the only
one he has a snowballs chance of getting even then it still
wouldn't give him an adequate chance of getting the rest.
__________________ The end always justify's the means by which they were brought to.
thanos has more experience with them than all the others and is more intelligent and resourceful than most, which means he can indeed take the gems from them.
So because he has more experience this leads you to believe that he can utilize the gems to their full capacity even though no one has ever been able to come close to doing it. And because i'm not entirely familiar with Robbins when he did it he had the advantage of having a gem himself as you said which Thanos doesn't and even if he could locate them how will he take the gems away?
__________________ The end always justify's the means by which they were brought to.
First, when Thanos first acquired then gems... He beat people more fomidable then this list here. Second, it has been stated on panel that Thanos can utilize the gems as good or better than anyone. Third, he can get the space gem and mind gem pretty easily. Despero wouldn't mind rape him, being that just as formidable TP's with the mind gem have already failed against Thanos. Despero durability is crap.. which means Thanos will get that gem. The space gem won't be much of an issue either. So Thanos with the Mind gem and Space gem.. will certainly acquire the others.
Moondragon couldn't read Thanos' mind because he was the paladin of the Reality Gem. Warlock made it so that no member of the Infinity Watch would be susceptible to Moondragon's telepathy.
I don't recall any other instance where anybody with the Mind Gem ever failed against Thanos.
His best chance by far is the reality gem, since Superboy Prime don't have the kind of powers to use it proficiently. After he gets this one, Despero will be his next target, since he's immune to mental attack.
If he go this way, he might succeed, but Darkseed will be a tough s.o.b to handle.
IIRC she also had the gem another time and couldn't read his mind, and in fact, lost the TP battle. Not to mention when she hasn't had the gem she, along with Xavier, mantis and other excellent TP users haven't been able to get into his mind.