Reference Custom Field on User Profile
You should expand the code in your question a little. 

First you need to get the assigned uid with something like:

$assigned_uid = $node-&gt;field_assigned_user[LANGUAGE_NONE][0]['target_id'];


Then you need to load the user object:

$assigned_user = user_load($assigned_uid);


Then you have access to the value:

$percentage_split = $user-&gt;field_percentage_split[LANGUAGE_NONE][0]['value'];


To help visualize the $node and $user objects and how to access the information, you can put the print_r() function into a php-enabled block in your footer. 

EDIT:

I looked at your code, and you should not try to do everything in a single statement. No wonder you are having problems. Break it out step by step like this:

// Get the assigned User ID from the node object

$assigned_uid = $node-&gt;field_assigned_user[LANGUAGE_NONE][0]['uid'];
// Load the user object for the assigned User.
$assigned_user = user_load($assigned_uid);
// Get the Percentage Split from the user object for the Assigned User (default to 0).
$percentage_split = (isset($assigned_user-&gt;field_percentage_split[LANGUAGE_NONE][0]['value'])) ? $assigned_user-&gt;field_percentage_split[LANGUAGE_NONE][0]['value'] : 0;
// Get the remaining values from the node object, defaulting to 0 if not there.
$other_ins = (isset($node-&gt;field_other_ins_[LANGUAGE_NONE][0]['value'])) ? $node-&gt;field_other_ins_[LANGUAGE_NONE][0]['value'] : 0;
$vb = (isset($node-&gt;field_vb[LANGUAGE_NONE][0]['value'])) ? $node-&gt;field_vb[LANGUAGE_NONE][0]['value'] : 0;
$finder_s_fee = (isset($node-&gt;field_finder_s_fee[LANGUAGE_NONE][0]['value'])) ? $node-&gt;field_finder_s_fee[LANGUAGE_NONE][0]['value'] : 0;
$broker_fee = (isset($node-&gt;field_broker_fee[LANGUAGE_NONE][0]['value'])) ? $node-&gt;field_broker_fee[LANGUAGE_NONE][0]['value'] : 0;
$dlc_franchise_fee_hst = (isset($node-&gt;field_dlc_franchise_fee_hst[LANGUAGE_NONE][0]['value'])) ? $node-&gt;field_dlc_franchise_fee_hst[LANGUAGE_NONE][0]['value'] : 0;

// Do the math.

$value = ($other_ins + $vb + $finder_s_fee + $broker_fee - $dlc_franchise_fee_hst ) * $percentage_split;


You also seem to be trying to use D6 data structures (won't work in D7), and it will also not work to try to give a function array keys.