Get structure pos.twig

{# Get the IDs of all the sections #}
{% set currentSectionId = entry.id %}
{% set allSectionIds = craft.entries.section('myStructure').level(1).ids() %}

{# Define var before loop #}
{% set sectionNumber = '' %}

{# Loop through all section IDs and find the one that matches the current #}
{% for key, sectionId in allSectionIds if sectionId == currentSectionId %}

    {# Use array key to calculate the section's position #}
    {% set sectionNumber = key + 1 %}

{% endfor %}

{# Credit: http://craftcms.stackexchange.com/questions/1779/display-number-based-on-position-in-structure-hierarchy/1781#1781 #}