$table->joins = array(
	array( 'select' => 'othertable.*', 'from' => array( 'myapp_othertable', 'othertable'), 'where' => "myapp_firsttable.id=othertable.other_id" )
);

How can I access to othertable fields on template row?

My table is generated with:

$table = new \IPS\Helpers\Table\Content...

but If I debug the object in template row I can't see "othertable" fields.

 

You'll probably have to use Custom table.

Or

use your content class in table Content and then join another table, like they do on members profile:

		$table = new \IPS\Helpers\Table\Content( $currentClass, $url, NULL, NULL, \IPS\Content\Hideable::FILTER_AUTOMATIC, 'read', FALSE );
		...
		$table->joins = array(
			array(
				'select' => "core_reputation_index.id AS rep_id, core_reputation_index.rep_date, core_reputation_index.rep_rating, core_reputation_index.member_received as rep_member_received, core_reputation_index.member_id as rep_member, core_reputation_index.reaction as rep_reaction",
				'from'   => 'core_reputation_index',
				'where'  => array( "core_reputation_index.type_id=" . $currentClass::$databaseTable . "." . $currentClass::$databasePrefix . $currentClass::$databaseColumnId  . " AND ( core_reputation_index.member_id=? OR core_reputation_index.member_received=? ) AND core_reputation_index.app=? AND core_reputation_index.type=?", $this->member->member_id, $this->member->member_id, $currentClass::$application, $currentClass::reactionType() ),
				'type'   => 'INNER'
			)
		);

$currentClass would be your content item class.