Chartruler is the ruler of the rising sign, as Venus di Sirius said, so Venus is your chartruler.
A planet in domicile, like your Jupiter in Sagittarius might be your sole dispositor, or the dispositor of a "chain of planets".
using classical rulers In your case:
Jupiter in Sagittarius
1st level
rules
a) Sun in Pisces
b) Saturn in Pisces
c) Pluto in Sagittarius
2nd level
a) Sun in Pisces
rules
Mars in Leo
b) Saturn in Pisces
rules
Moon and Venus in Capricorn, Neptune and Uranus in Capricorn, Mercury in Aquarius
3rd level
a) Mars in Leo
rules
nothing
b) Venus in Capricorn
rules
nothing
c) Mercury in Aquarius
rules
(Chiron in Virgo, if you want to consider it)
d) Moon in Capricorn
rules
nothing
You can see that Jupiter in Sagittarius is on the top of a chain, with all planets being involved, so Jupiter is called "sole dispositor" in your chart.
In other charts there might be more "dispositor - chains".
For example in my own chart, Jupiter in Pisces is the head of his own dispositor chain including the more intellectual planets in my chart.
the mutual reception of Moon and Saturn is the head of another dispositor chain, including my emotional and relational planets.
Others might have several planets in their own signs and have even more dispositor chains.
Anyway, even though Jupiter is not your chartruler, it will have a big influence, maybe be more influential than you would have thought before.
though I tend to think you have to consider Jupiter in a team with Saturn, as Saturn is the direct dispositor of 3 personal planets (Moon-Venus-Mercury).