As moritz said, this isn't OO, but the second line will work with one small modification:

print "$BldEnv{TTT2}->{VersionTwo}\n";
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Your version didn't work because the first -> was trying to dereference $BldEnv as though it were a reference to a hash. But WAIT! $BldEnv doesn't exist! You declared %BldEnv. Different animal! Despite using the $ sigil to get at hash values, when you added the -> after it, Perl was looking for a SCALAR variable and ignoring the HASH that you defined!

Perl's syntactic sugar allows you to get around derefencing the 'TTT2' hash using ->. As such, the first one is better.

Further to this, you really don't need to do string interpolation... can get a little messy with multi-level data structures. You could just do:

print $BldEnv{TTT2}{VersionTwo},"\n";
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That way the variable is easier to see and prevents a number of interpolation pitfalls. If you're feeling adventurous, you could install the Perl6::Say module so you don't have to append that "\n" to the end like so:

use Perl6::Say;
say $BldEnv{TTT2}{VersionTwo};
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The "\n" is auto-appended by say.

What you should _definately_ always do do is begin each script with:

use strict;
use warnings;
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This would have thrown an error on your last print statement telling you that you that $BldEnv hadn't been declared, cluing you in that you're doing something wrong.

Happy Perl-ing!

update: expanded on difference between $BldEnv{key} and $BldEnv->{key}.

update the second: fixed errorneous variable naming.