First you have to add a field uom_id to product.attribute.line class, and also you have to write a default function to get the value of uom with respect to product template. Also you have to mention the uom_id in tree view inside the product_view.xml .

I don't want to add uom on product attribute line but on product attribute (because uom is the same for each attribute line). To do that I had already code py file:

# -*- coding: utf-8 -*-
from openerp import models, fields
class ProductAttribute(models.Model):
    _name = 'product.attribute'    
    _inherit = 'product.attribute'
    uom_id = fields.Many2one('product.uom', 'Unit of Measure')

and the follow xml code:

<?xml version="1.0" encoding="utf-8"?>
<openerp>  
<data>
    <!-- Unit of Measure on Attributes Configuration -->
    <record id="attribute_uom_tree_view" model="ir.ui.view"> 
        <field name="name">product.attribute.tree.type</field>      
        <field name="model">product.attribute</field>      
        <field name="inherit_id" ref="product.attribute_tree_view"/>      
            <field name="arch" type="xml">        
            <field name="name" position="after">          
                <field name="uom_id"/>        
            </field>      
        </field>    
    </record>
</data>
</openerp>

 Now (in my understand of odoo) I need to find the page which display the table and add the column on tree view.

[edit 21 nov]

Finally I have found the solution. Add model relation:

class ProductAttributeLine(models.Model):
    _inherit = 'product.attribute.line' uom_id = fields.Many2one(related='attribute_id.uom_id', string='Unit of Measure', store=False, readonly=True)

 <record id="product_variant_list_view" model="ir.ui.view"> <field name="name">product.template.variant.form</field> <field name="model">product.template</field> <field name="type">form</field>  <field name="inherit_id" ref="product.product_template_only_form_view" />  <field name="arch" type="xml">    <field name="value_ids" position="after">     <field name="uom_id" />   </field> </field> </record>